Water-absorbing agent and production process therefor, and water-absorbent structure

ABSTRACT

The present invention provides: a novel water-absorbing agent, which exhibits an excellent absorption capacity under a load (AAP), gel layer liquid permeation rate under a load (FRUP), saline flow conductivity (SFC), and shape-maintaining property and ball burst strength (BBS) of a swollen water-absorbing agent aggregate, and excellent persistency of these effects for a long time. The water-absorbing agent, which comprises a polymer obtained by a process including the steps of polymerizing and then crosslinking a monomer including acrylic acid and/or a salt thereof, with the water-absorbing agent being characterized by: (1) exhibiting a free swelling capacity of not less than 23 g/g (GV), a gel deformation of not more than 12.5 cm under a short-time load (0.5 hrPT), and a gel deformation deterioration of not more than 3.5 cm under a load with the passage of time (ΔPT); (2) exhibiting a free swelling capacity of not less than 23 g/g (GV), a ball burst strength of not less than 80 gf (BBS), and a deterioration of ball burst strength of not more than 40% (DBBS); or (3) exhibiting a free swelling capacity of not less than 23 g/g (GV), an absorption capacity of not less than 20 g/g under a load of 4.9 kPa (AAP), and a gel deformation of not more than 12.5 cm under a load (16 hrPT).

This application is a divisional of U.S. patent application Ser. No.10/053,659, filed Jan. 24, 2002, now U.S. Pat. No. 7,098,284.

BACKGROUND OF THE INVENTION

A. Technical Field

This invention relates to a novel water-absorbing agent, a productionprocess therefor, and a water-absorbent structure.

B. Background Art

In recent years, water-absorbent resins are widely used as constituentmaterials of water-absorbent articles, such as disposable diapers,sanitary napkins, and so-called incontinent pads, for the purpose ofcausing the water-absorbent resins to absorb body fluids. Known examplesof the above water-absorbent resins are disclosed in Japan IndustrialStandard (JIS) K7223-1996. Examples of the known water-absorbent resinsinclude: crosslinked products of partially neutralized polyacrylicacids; hydrolyzed products of starch-acrylic acid graft polymers,saponified products of vinyl acetate-acrylic acid ester copolymers,hydrolyzed products of acrylonitrile- or acrylamide copolymers, andcrosslinked products thereof; and crosslinked polymers of cationicmonomers.

The water-absorbent resins are hardly used alone because they aregenerally powders. They are mixed with hydrophilic cellulose fibers,such as pulverized pulps and paper, and used as water-absorbentstructures such as disposable diapers (for example, U.S. Pat. No.3,888,257). When the water-absorbent resins alone are used for absorbingmuch water in a short time, they cannot absorb in a short time.Therefore, the above mixing is particularly required in order to preventthe water from spreading. The cellulose fibers have functions of:retaining powdery absorbent-reins, or sufficiently spreading water tothe water-absorbent resins that are distributed according to capillaryaction, or retaining swollen water-absorbent resins after water isabsorbed.

However, when water-absorbent structures as obtained by the above artare used as disposable diapers, and when the ratio of the absorbentresin particles to the cellulose fibers is higher, the cohesive strengthis weak among the cellulose fibers. Therefore, the water-absorbentstructures have the following problems: the absorption properties arenot as sufficient as expected because the absorbent resins as swollenare moved and dropped after they absorb urine in practical use; and theabsorption structures do not display the aimed properties because thedecomposition of the absorbent resin particles is caused by a certainkind of component in the urine.

Heretofore, many proposals have been made to solve the above problems.Hereinafter, their artificial contents and problems are described.

JP-A-31362/1993 discloses a method which involves: treating a surface ofa water-absorbent resin particle having a carboxyl group with acrosslinking agent having two or more functional groups which can form acovalent bond by reacting with the carboxyl group in order to crosslinkwith a portion of the carboxyl groups; and thereafter blending theparticle with a cationic polymer compound which can form an ionic bondby reacting with the carboxyl group and has a weight-average molecularweight of not less than 2,000.

Japanese Patent No. 3017584 discloses a method for producing awater-absorbent -structure, wherein the water-absorbent structureincludes a water-absorbent resin particle of which the surface has anacidic group, a cellulose fiber, and a cationic polymer compound havinga weight-average molecular weight of not less than 2,000.

U.S. Pat. No. 5,382,610 discloses a method which involves: treating asurface of a water-absorbent resin particle having a carboxyl group witha crosslinking agent having two or more functional groups which can forma covalent bond by reacting with the carboxyl group in order tocrosslink with a portion of the carboxyl groups; and thereafter blendingthe particle with a cationic polymer compound which can form an ionicbond by reacting with the carboxyl group and has a weight-averagemolecular weight of not less than 2,000, and a method which involvesproducing a water-absorbent structure which comprises a water-absorbentresin particle of which the surface has an acidic group, a cellulosefiber, and a cationic polymer compound having a weight-average molecularweight of not less than 2,000.

Japanese Patent No. 3107909 discloses a particulate water-absorbingagent having the following properties: the ratio of the particles havingparticle diameters of not larger than 149 μm is less than 10 weight. %;and the water-absorbing agent exhibits an absorption rate of 20 to 90seconds when 28 g of physiological saline is absorbed in thewater-absorbing agent (g), with the water-absorbing agent beingcharacterized in that: when an iron ball (a ball as described in JISB-1501) having a diameter of 15/32inch (about 11.9 cm) freely falls froma point having a height of 20 cm to the swollen hydrogel as obtained inthe above way, the iron ball bounds on the swollen hydrogel, or theswollen hydrogel is not invaded by the iron ball (about 11.9 cm) afterthe iron ball stands still.

JP-A-227435/1990 discloses a liquid-absorbent polymer composition, whichcomprises a base polymer particle having a absorption rate of not morethan 20 seconds, substantially water-absorbency, and an absorptioncapacity of at least 30 ml/g under an ordinary pressure, and issurface-crosslinked with a multivalent ionic crosslinking agent, and isgranulated so that the particle size of the polymer composition will belarger than that of the base polymer particle, with the liquid-absorbentpolymer composition being characterized by having the particledistribution such that: the liquid-absorbent polymer particle does notsubstantially include a particle larger than 300 μm before theliquid-absorbent polymer particle is surface-crosslinked and granulated,and 40% or more of the particles have particle diameters of not largerthan 150 μm.

JP-A-53550/1996 discloses a method for producing a high-water-absorbentresin, which involves: adding (a) a hydrophilic polymer and (b) acrosslinking agent into a high-water-absorbent resin hydrogel, whereinthe high-water-absorbent resin hydrogel is obtained by adding 10 to 100parts by weight of water to 100 parts by weight of ahigh-water-absorbent resin, wherein the hydrophilic polymer has areactive group and the amount of the hydrophilic polymer is 0.005 to 5parts by weight per 100 parts by weight of the high-water-absorbentresin, and wherein the crosslinking agent has two or more functionalgroups reactable with the hydrophilic polymer having the reactive groupand the weight ratio of the hydrophilic polymer/crosslinking agent is inthe range of 0.1 to 30; blending them together; and carrying out aheating reaction of them.

Water-absorbent resins as modified by these known arts are certainlydifficult to move or drop when they are combined with cellulose fibers.In addition, the swollen water-absorbing agent aggregate may also havean excellent shape-maintaining property and ball burst strength (BBS).In the present invention, the “swollen water-absorbing agent aggregate”means a state such that water-absorbing agents as swollen come intocontact with one another after absorbing water, and can be regarded asone lump, for example, a state such that the cohesive strength of suchas ionic bond, hydrogen bond, covalent bond, and coordinate bond isapplied among swollen water-absorbing agents, and the swollenwater-absorbing agents come into contact with one another. However, thewater-absorbent resin particles and/or water-absorbing agents do nothave a sufficient absorption amount of water under a load (absorptioncapacity under a load (AAP)), gel layer liquid permeation rate under aload (FRUP), saline flow conductivity (SFC). Therefore, when they werecombined with cellulose fibers or other materials, the absorptionproperties could not be said to be sufficient. For example, when thewater-absorbing agents were used as a portion of a water-absorbentstructure in disposable diapers, they had a low absorption capacityunder a load (AAP). Therefore, they had the following serious problems:a demerit such that the urine as absorbed in the water-absorbentstructure is returned to the surface of the diaper when the pressure isexerted by body weight; and a demerit such that the water-absorbentstructure has a low liquid permeability therein because the gel layerliquid permeation rate under a load (FRUP) and the saline flowconductivity (SFC) are not sufficient, and therefore, the liquid doesnot spread enough in the water-absorbent structure, and the decrease ofthe absorption amount of water and the leak of the liquid are caused.

In addition, the above water-absorbent resins as modified by these knownarts are certainly difficult to move or drop when they are combined withcellulose fibers. In addition, the swollen water-absorbing agentaggregate may also have an excellent shape-maintaining property and ballburst strength (BBS). However, its absorption properties are graduallylost with the passage of time after it absorbs water, and particularlythere was a demerit such that the shape-maintaining property and ballburst strength (BBS) of the swollen water-absorbing agent aggregate wereconsiderably lowered. Because these are lowered, when disposal diaperscomprising a water-absorbent resin in a high ratio are especially usedfor a long time, it results in moving the resultant swollen gel andlowing absorption properties.

WO 97/03114 discloses a method for producing a water-absorbing agentpowder, which is characterized by decreasing a residual crosslinkingagent by adding a nucleophilic agent to a carboxyl-group-containingwater-absorbent resin powder of which the surface neighborhood issurface-crosslinked with a crosslinking agent including an epoxy groupand in which the crosslinking agent remains, wherein the water-absorbentresin powder is in a state of heated powder. In Example 1 as describedin this document, an example of adding polyethylenimine as anucleophilic agent to a water-absorbent resin powder is described.

JP-A-509591/1997 and WO 95/22356 disclose an absorbing material havingan improved absorbency, which includes a mixture of: (1) two or moreabsorbent gel-formable particles which are water-insoluble and include awater-swellable polymer; and (2) an absorbency-improved polymerreactable with at least one component included in urine, with thewater-absorbing material being characterized in that the mixture isproduced by: (i) applying a solution onto the two or more absorbentgel-formable particles, wherein the solution includes an organic solvent(favorably, polar organic solvent), water, and the absorbency-improvedpolymer, and the weight ratio between the organic solvent and the wateris at least 50:50, favorably in the range of 70:30 to 98:2; and (ii)removing a portion of the organic solvent and water from these appliedabsorbent gel-formable particles. In Examples as described in thisdocument, an example of adding polyallylamine to a water-absorbent resinpowder is described.

JP-A-342963/2000 discloses a method for producing an absorbing agentcomposition, which is characterized by adding a polyamine compoundhaving a weight-average molecular weight of not less than 5,000 to awater-absorbent resin having an diffusive absorption capacity of notless than 25 g/g in an aqueous sodium chloride solution of 0.9 weight %after 60 minutes from the start of swelling under a load of 20 g/cm²(1.96 kPa).

WO 96/17884 discloses a water-absorbent resin composition having awater-holding ability of not less than 20 g/g, an absorption rate of notmore than 120 seconds, a liquid permeation rate of not more than 200seconds under a load. In Example 19 as described in this document, anexample of adding polyethylenimine to a water-absorbent resin particleis described.

JP-A-290000/1997 discloses an absorbing material that comprises (a) anabsorbent gel particle including a water-insoluble absorbenthydrogel-formable polymer, (b) a polycationic polymer, (c) a glue finefiber, and (d) a carrier layer, with the absorbing material beingcharacterized in that the polycationic polymer is bonded to theabsorbent gel particle and the glue fine fiber acts as an adhesive agentbetween the absorbent gel particle and the carrier layer.

Even in these technical arts, the cationic polymer compound as blendedwith the water-absorbent resin particle is not sufficiently crosslinked,or the gel layer permeation rate under, a load (FRUP) or the saline flowconductivity (SFC) of the water-absorbent resin particle is notsufficient. Therefore, the absorption properties could not be said to besufficient in the same reason as of the above. In addition, as to theswollen water-absorbing agent aggregate, its absorption properties aregradually lost with the passage of time after it absorbs water, andthere was particularly a demerit such that the shape-maintainingproperty and ball burst strength (BBS) of the swollen water-absorbingagent aggregate were considerably lowered.

JP-A-3123/1997 discloses a water-absorbent polymer characterized bydisplaying a delay bonding character in contact with a water-containingliquid. Even in this technical art, the gel layer permeation rate undera load (FRUP) or the saline flow conductivity (SFC) of a water-absorbentresin particle is not sufficient. Therefore, the absorption propertiescould not be said to be sufficient in the same reason as of the above.In addition, there was a demerit such that: the absorption capacity of awater-absorbing agent under a load (AAP) was not sufficient wherein thewater-absorbing agent was obtained by blending the water-absorbent resinparticle and a polyamine together; and the urine as absorbed in awater-absorbent structure was returned to the surface of a diaper whenthe pressure was exerted by body weight.

WO 97/12575 discloses a technical art to improve a gel layerpermeability under a load by carrying out a reaction between awater-insoluble water-absorbing hydrogel-formable polymer and apolycationic polymer, and forming a covalent bond between both of them.However, there was a demerit such that the shape-maintaining propertyand ball burst strength (BBS) of a swollen water-absorbing agentaggregate were considerably lowered because the covalent bond was formedbetween both of them by heating. In addition, the gel layer permeationrate under a load (FRUP) or the saline flow conductivity (SFC) of awater-absorbent resin particle is not sufficient. Therefore, theabsorption properties could not be said to be sufficient in the samereason as of the above.

In WO 99/34841, WO 99/34842, WO 99/34843, and WO 99/25393, anacidic-group-containing water-insoluble swellable polymer and abasic-group-containing water-insoluble swellable polymer are mixedtogether and used. Accordingly, when the resultant polymer comes intocontact with saline, the salt in the saline is absorbed into the polymerand the respective acid group and base group are neutralized with thesalt. Therefore, the following properties are sufficiently generalized:an absorption capacity under a load (AAP), a saline flow conductivity(SFC), and a shape-maintaining property and a ball burst strength (BBS)of a swollen water-absorbing agent aggregate. However, the ratio of theacidic group and the basic group is important in this technical art, andit is very uneconomical because the valuable basic water-insolubleswellable polymer must be used in a large amount (usually, the amount isnearly equal to that of the acidic-group-containing water-insolubleswellable polymer, at least not less than 10 weight %). In addition,there was a demerit such that the absorption amount of water wasextremely lowered in a liquid not including salt or in the presence ofmore salt than the amount possible to neutralize. Furthermore, there wasusually a demerit such that the free swelling capacity (GV) of thewater-absorbing agent as obtained in the above technical art was notsufficient.

JP-A-95955/2000 discloses a water-absorbing agent composition comprisingat least a water-absorbent resin particle having an anionic dissociativegroup and a water-swellable resin particle having a cationic group, withthe water-absorbing agent composition being characterized in that: 45 to90 mol % of the anionic dissociative groups of the water-absorbent resinparticle are neutralized; the weight ratio (α) of the water-absorbentresin particle having the anionic dissociative group relative to thetotal weight of the water-absorbent resin particle having the anionicdissociative group and the water-swellable resin particle having thecationic group is at least 0.8; and the absorption capacity of thewater-absorbing agent composition under a load (P) is at least 20 g/g.The water-absorbing agent as obtained by this technical art has asufficient absorption capacity under a load (AAP) and saline flowconductivity (SFC). However, the water solubility of the water-swellableresin particle having the cationic group as used in this technical artis low. Therefore, there was a demerit such that the shape-maintainingproperty and ball burst strength (BBS) of a swollen water-absorbingagent aggregate were considerably lowered.

SUMMARY OF THE INVENTION

A. Object of the Invention

The following absorbent resin is ideal when it is practically used: anabsorbent resin, which exhibits an excellent absorption capacity under aload (AAP), gel layer liquid permeation rate under a load (FRUP), andsaline flow conductivity (SFC), and sufficiently brings out synergismwith a partner material to be combined with, such as cellulose fibers,and has an excellent shape-maintaining property or ball burst strength(BBS) of a swollen water-absorbing agent aggregate, and maintains theseeffects for a long time. However, this has not been obtained yet underthe present circumstances.

B. Disclosure of the Invention

As a means of solving the above problems, this invention first provides:a production process for a water-absorbing agent, which comprises thestep of blending 100 parts by weight of water-absorbent resin particles(A) and 0.01 to 10 parts by weight of a cationic polymer compound (B)together, wherein the cationic polymer compound (B) is obtained by aprocess including the step of crosslinking a cationic polymer with acrosslinking agent of which the amount is 0.01 to 10 weight % of thecationic polymer, and wherein the cationic polymer compound (B) has awater solubility of 70 to 10 weight % if the cationic polymer compound(B) is obtained from an ethylenimine monomer, otherwise the cationicpolymer compound (B) has a water solubility of 100 to 10 weight %.

The present invention secondly provides: a production process for awater-absorbing agent, which comprises the step of blending 100 parts byweight of water-absorbent resin particles (A) and 0.01 to 10 parts byweight of a cationic polymer compound (B) together, wherein thewater-absorbent resin particles (A) exhibit an absorption capacity ofnot less than 20 g/g under a load of 4.9 kPa (AAP) and a gel layerliquid permeation rate of not more than 800 seconds under a load (FRUP),and wherein the cationic polymer compound (B) has a water solubility of100 to 10 weight %

The present invention thirdly provides: a production process for awater-absorbing agent, which comprises the step of blending 100 parts byweight of water-absorbent resin particles (A) and 0.01 to 10 parts byweight of a cationic polymer compound (B) together, wherein thewater-absorbent resin particles (A) exhibit an absorption capacity ofnot less than 20 g/g under a load of 4.9 kPa (AAP) and a saline flowconductivity of not less than 20 (10⁻⁷×cm³×s×g⁻¹) (SFC), and wherein thecationic polymer compound (B) has a water solubility of 100 to 10 weight%.

The present invention fourthly provides: a water-absorbing agent, whichis obtained by the production process for a water-absorbing agentaccording to the present invention.

The present invention fifthly provides: a water-absorbing agent, whichcomprises water-absorbent resin particles (A) and a cationic polymercompound (B), wherein the cationic polymer compound (B) is substantiallyionically bonded to the water-absorbent resin particles (A), with thewater-absorbing agent being characterized by exhibiting a free swellingcapacity of not less than 23 g/g (GV), an absorption capacity of notless than 20 g/g under a load of 4.9 kPa (AAP), and a saline flowconductivity of not less than 50 (10⁻⁷×cm³×s×g⁻¹) (SFC).

The present invention sixthly provides: a water-absorbing agent, whichcomprises a polymer obtained by a process including the steps ofpolymerizing and hen crosslinking a monomer including acrylic acidand/or a salt thereof, with the water-absorbing agent beingcharacterized by exhibiting a free swelling capacity of not less than 23g/g (GV), an absorption capacity of not less than 20 g/g under a load of4.9 kPa (AAP), and a gel deformation of not more than 12.5 cm under aload (16 hrPT).

The present invention seventhly provides: a water-absorbing agent, whichcomprises a polymer obtained by a process including the steps ofpolymerizing and then crosslinking a monomer including acrylic acidand/or a salt thereof, with the water-absorbing agent beingcharacterized by exhibiting a free swelling capacity of not less than 23g/g (GV), an absorption capacity of not less than 20 g/g under a load of4.9 kPa (AAP), and a 16 hours' ball burst strength of not less than 80gf (16 hrBBS).

The present invention eighthly provides: a water-absorbing agent, whichcomprises a polymer obtained by a process including the steps ofpolymerizing and then crosslinking a monomer including acrylic acidand/or a salt thereof, with the water-absorbing agent beingcharacterized by exhibiting a free swelling capacity of not less than 23g/g (GV), a gel deformation of not more than 12.5 cm under a short-timeload (0.5 hrPT), and a gel deformation deterioration of not more than3.5 cm under a load with the passage of time (ΔPT).

The present invention ninthly provides: a water-absorbing agent, whichcomprises a polymer obtained by a process including the steps ofpolymerizing and then crosslinking a monomer including acrylic acidand/or a salt thereof, with the water-absorbing agent beingcharacterized by exhibiting a free swelling capacity of not less than 23g/g (GV), a ball burst strength of not less than 80 gf (BBS), and adeterioration of ball burst strength of not more than 40% (DBBS).

The present invention tenthly provides: a water-absorbent structure,which comprises the water-absorbing agent as obtained in the presentinvention.

These and other objects and the advantages of the present invention willbe more fully apparent from the following detailed disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic section of a measurement apparatus as used formeasuring the gel layer liquid permeation rate under a load (FRUP),which is one of the properties as displayed by the water-absorbent resinparticles (A) in the present invention.

FIG. 2 is a schematic section of one measurement apparatus as used formeasuring the gel deformation under a load (16 hrPT) or gel deformationunder a short-time load (0.5 hrPT) which is one of the properties asdisplayed by the water-absorbing agent in the present invention, whereinthe apparatus is used for forming swollen water-absorbing agentaggregates.

FIG. 3 is a schematic upper view of one measurement apparatus as usedfor measuring the gel deformation under a load (16 hrPT) or geldeformation under a short-time load (0.5 hrPT) which is one of theproperties as displayed by the water-absorbing agent in the presentinvention, wherein the apparatus is used for storing swollenwater-absorbing agent aggregates.

FIG. 4 is a schematic section of one measurement apparatus as used formeasuring the gel deformation under a load (16 hrPT) or gel deformationunder a short-time load (0.5 hrPT) which is one of the properties asdisplayed by the water-absorbing agent in the present invention, whereinthe apparatus is used for pressurizing swollen water-absorbing agentaggregates.

FIG. 5 is a schematic upper view of one image example when measuring thegel deformation under a load (16 hrPT) or gel deformation under ashort-time load (0.5 hrPT) which is one of the properties as displayedby the water-absorbing agent in the present invention, wherein the oneexample shows deformed swollen water-absorbing agent aggregates asobtained after swollen water-absorbing agent aggregates are pressurized.

FIG. 6 shows image examples before and after pressurization whenmeasuring the gel deformation under a load (16 hrPT) which is one of theproperties as displayed by the water-absorbing agent in the presentinvention, and shows examples of swollen water-absorbing agentaggregates and deformed swollen water-absorbing agent aggregates asobtained after pressurization. Herein, a water-absorbing agent 1 iscompared with a comparative water-absorbing agent 2, and FIG. 6 is anupper view of these.

FIG. 7 is a schematic section of a measurement apparatus as used formeasuring the saline flow conductivity (SFC).

FIG. 8 is an illustrative view of a measurement apparatus as used forpreparing a predetermined layer of swollen water-absorbing agents.

FIG. 9 is an illustrative view of a measurement apparatus as used formeasuring a ball burst strength value (BBS) of water-absorbing agents.

EXPLANATION OF THE SYMBOLS

-   A Swollen water-absorbent resin particles-   B Weight-   C Round plate-   D Pressurizing rod-   H Glass filter-   I Pressurizing plate having glass filter-   J Physiological saline-   K Glass column having cock-   L Standard line (liquid surface having a liquid height of 150 mm)-   M Standard line (liquid surface having a liquid height of 100 mm)-   1 Round-dish-like (Petri-dish-like) receptacle-   2 Swollen water-absorbing agent aggregate-   3 Round cover-   4 Weight-   5 Sealable plastic bag-   6 Weight-   7 Deformed swollen water-absorbing agent aggregate-   8 Straight distance between two points, where the straight distance    will be the longest from one arbitrary end to the other arbitrary    end-   31 Tank-   32 Glass tube-   33 Aqueous sodium chloride solution of 0.69 weight %-   34 L-tube having cock-   35 Cock-   40 Receptacle-   41 Cell-   42 Stainless wire mesh-   43 Stainless wire mesh-   44 Swollen gel-   45 Glass filter-   46 Piston-   47 Holes in piston-   48 Collecting receptacle-   49 Balance-   210 Stainless weight-   220 Inner-cylinder cover plate-   230 Out-side cylinder-   240 Teflon flat-bottomed tray-   250 No. 400 mesh stainless-steel screen-   260 Water-absorbing agent layer-   270 Inner-cylinder-   280 Circular lower sample clamp platen-   290 Polished stainless steel ball-shaped prove-   300 Circular upper sample clamp platen-   310 Stationary crosshead-   320 Moving crosshead-   330 Force sensing load cell

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, the following abbreviations are used in the explanation ofthe present invention.

Free swelling capacity: hereinafter, abbreviated to GV.

Absorption capacity under a load of 4.9 kPa: hereinafter, abbreviated toAAP.

Gel layer permeation rate under a load: hereinafter, abbreviated toFRUP.

Saline flow conductivity: hereinafter, abbreviated to SFC.

Gel deformation under a short-time load: hereinafter, abbreviated to 0.5hrPT.

Gel deformation under a load: hereinafter, abbreviated to 16 hrPT.

Gel deformation deterioration under a load with the passage of time:hereinafter, abbreviated to ΔPT.

Ball burst strength: hereinafter, abbreviated to BBS.

16 hours' ball burst strength: hereinafter, abbreviated to 16 hrBBS.

Deterioration of ball burst strength: hereinafter, abbreviated to DBBS.

In the above abbreviations, GV is an acronym of Gel Volume, and AAP isan acronym of Absorbency Against Pressure, and FRUP is an acronym ofFlow Rate Under Pressure, and SFC is an acronym of Saline FlowConductivity, and PT is an acronym of Pressure Test, and BBS is anacronym of Ball Burst Strength, and DBBS is an acronym of Deteriorationof Ball Burst Strength.

Incidentally, these values are measured according to measurement methodsas shown below.

The present invention relates to a water-absorbing agent from awater-absorbent resin, a production process therefor, and awater-absorbent structure. Incidentally, the water-absorbing agent inthe present invention means a modified polymer water-absorbing agentcomprising a major proportion of a water-absorbent resin (favorably inthe range of not less than 70 weight %, more favorably in the range ofnot less than 80 weight %), or its composition. The water-absorbentresin is a gel-formable resin that has crosslinking structure, and iswater-insoluble, and includes a water-swellable polymer.

—Water-absorbent Resin Particles (A)—

Hereinafter, the water-absorbent resin particles (A), which are used inthe present invention, are explained in the first place.

The water-absorbent resin particles (A) usable in the present inventionfavorably exhibit an AAP of not less than 20 g/g, more favorably notless than 22 g/g, still more favorably not less than 25 g/g, yet stillmore favorably not less than 27 g/g, most favorably not less than 30g/g. When the AAP is not less than 20 g/g, and when the water-absorbingagent according to the present invention is partially used as awater-absorbent structure of disposable diapers, the urine as absorbedin the water-absorbent structure is very effectively prevented fromreturning to the surface of the diaper.

In addition, the water-absorbent resin particles (A) favorably exhibit aFRUP of not more than 1,500 seconds, more favorably not more than 1,200seconds, still more favorably not more than 800 seconds, yet still morefavorably not more than 500 seconds, particularly favorably not morethan 300 seconds, most favorably not more than 150 seconds. In addition,the water-absorbent resin particles (A) favorably exhibit a SFC of notless than 20 (10⁻⁷×cm³×s×g⁻¹), more favorably not less than 25(10⁻⁷×cm³×s×g⁻¹), still more favorably not less than 35(10⁻⁷×cm³×s×g⁻¹), yet still more favorably not less than 50(10⁻⁷×cm³×s×g⁻¹), most favorably not less than 75 (10⁻⁷×cm³×s×g⁻¹). TheFRUP and SFC of the water-absorbent resin particles (A) have a greatinfluence on liquid permeability of the water-absorbing agent asobtained in the present invention after the water-absorbing agent isswollen. That is to say, if the water-absorbing agent according to thepresent invention is produced and favorably the FRUP of thewater-absorbent resin particles (A) is adjusted to not more than 1,500seconds and/or the SFC of the water-absorbent resin particles (A) isadjusted to not less than 20 (10⁻⁷×cm³×s×g⁻¹), the following effects areremarkably improved: when the water-absorbing agent according to thepresent invention is partially used as a water-absorbent structure ofdisposable diapers, the liquid permeability is improved, and the liquidspreads enough in the water-absorbent structure, and the absorptionamount of water is increased, and the leak of the liquid is prevented.

The water-absorbent resin particles (A) favorably used in the presentinvention, for example, can be produced by carrying out a specificsurface-crosslinking treatment in the neighborhood of the particle of awater-absorbent resin (hereinafter, referred as simply “water-absorbentresin”) that is a precursor.

Examples of the water-absorbent resin include at least one kind selectedfrom the group consisting of: partially-neutralized and crosslinkedpoly(acrylic acids); hydrolyzed graft polymers of starch-acrylonitrile;hydrolyzed graft polymers of starch-acrylic acid; saponified copolymersof vinyl acetate-acrylic acid ester; and hydrolyzed copolymers ofacrylonitrile or acrylamide, or crosslinked polymers of these hydrolyzedcopolymers thereof; modified products of crosslinked poly(vinyl alcohol)including a carboxyl group; and copolymers of crosslinkedisobutylene-maleic anhydride. These water-absorbent resins can be usedeither alone respectively or in combinations with each other. Amongthese, the water-absorbent resins having a carboxyl group are favorableeither alone respectively or in combinations with each other. Thewater-absorbent resins typically comprise a major proportion of polymersobtained by a process including the step of polymerizing and thencrosslinking monomers including acrylic acid and/or its salt(neutralized product) as a main component. Examples thereof aredisclosed in the following way: partially-neutralized and crosslinkedpoly(acrylic acids) (U.S. Pat. Nos. 4,625,001, 4,654,039, 5,250,640,5,275,773, and EP 456136); crosslinked and partially-neutralized graftpolymers of starch-acrylic acid (U.S. Pat. No. 4,076,663); copolymers ofisobutylene-maleic acid (U.S. Pat. No. 4,389,513); saponified copolymersof vinyl acetate-acrylic acid (U.S. Pat. No. 4,124,748); hydrolyzed(co)polymers of acrylamide (U.S. Pat. No. 3,959,569); and hydrolyzedpolymers of acrylonitrile (U.S. Pat. No. 3,935,099).

In addition, the above water-absorbent resin as used has a crosslinkingstructure, and favorably exhibits an uncrosslinked water-extractablecontent of not more than 25 weight %, more favorably not more than 20weight %, still more favorably not more than 15 weight %, particularlyfavorably not more than 10 weight %.

Acrylic acid (salt), namely, acrylic acid and/or its salt (neutralizedproduct) is favorably used as a component comprised in the abovewater-absorbent resin. Examples of the acrylic acid salt include:acrylic acid salts of alkaline metal, such as sodium, potassium, andlithium; acrylic acid ammonium salts, and acrylic acid amine salts. Theacrylic acid sodium salt is favorable. The constituent units of a majorproportion of the above water-absorbent resin favorably comprise acrylicacid in the range of 0 to 50 mol % and a salt thereof in the range of100 to 50 mol % (wherein the total of them is 100 mol %), and morefavorably comprise acrylic acid in the range of 10 to 40 mol % and asalt thereof in the range of 90 to 60 mol % (wherein the total of themis 100 mol %). The neutralization of the water-absorbent resin to formthe salt may be carried out in a state of monomers beforepolymerization, or in a state of polymers in the course of or afterpolymerization, or in combinations of each other. When theneutralization is carried out in a state of polymers, there areadvantages in decreasing the water-extractable content. However, ittakes fairly much time to carry out the neutralization. Therefore, it isfavorable that the neutralization is carried out in a state of monomersbefore polymerization in view of production costs.

The monomers to obtain the water-absorbent resin as used in the presentinvention may comprise other monomers in addition to the acrylic acid(salt) when the occasion demands. The monomers other than the acrylicacid (salt) are not especially limited, but examples thereof include:anionic unsaturated monomers, such as methacrylic acid, maleic acid,vinylsulfonic acid, styrenesulfonic acid,2-(meth)acrylamido-2-methylpropanesulfonic acid,2-(meth)acryloylethanesulfonic acid, and 2-(meth)acryloylpropanesulfonicacid, and their salts; nonionic unsaturated monomers containing ahydrophilic group, such as acrylamide, methacrylamide,N-ethyl(meth)acrylamide, N-n-propyl(meth)acrylamide,N-isopropyl(meth)acrylamide, N,N-dimethyl(meth)acrylamide,2-hydroxyethyl(meth)acrylate, 2-hydroxypropyl(meth)acrylate,methoxypolyethylene glycol(meth)acrylate, polyethylene glycolmono(meth)acrylate, vinylpyridine, N-vinylpyrrolidone,N-acryloylpiperidine, N-acryloylpyrrolidine, and N-vinylacetamide;cationic unsaturated monomers such asN,N-dimethylaminoethyl(meth)acrylate,N,N-diethylaminoethyl(meth)acrylate,N,N-dimethylaminopropyl(meth)acrylate,N,N-dimethylaminopropyl(meth)acrylamide, and their quaternary salts.These monomers may be used either alone respectively or in combinationswith each other.

In the present invention, when the monomers other than the acrylic acid(salt) are used, the ratio is favorably not more than 30 mol %, morefavorably not more than 10 mol %, of the total amount of the acrylicacid and its salt. If the above monomers other than acrylic acid (salt)are used in the above ratio, then the absorption properties of theresultant water-absorbent resin (A) are still more improved, and thewater-absorbent resin (A) can be obtained at a still lower cost.

When the above monomers are polymerized in order to obtain thewater-absorbent resin as used in the present invention, the bulkpolymerization or precipitation polymerization can be carried out.However, in view of the performance or the easiness of thepolymerization control and further the liquid permeability of swollengels, the aqueous solution polymerization or reversed-phase suspensionpolymerization is favorably carried out using the above hydrophilicmonomer in the form of its aqueous solution. Incidentally, when themonomer is used in the form of its aqueous solution, the concentrationof the monomer in its aqueous solution (hereinafter referred to as“aqueous monomer solution”) depends upon the temperature of the aqueoussolution or the monomer, and is not especially limited, but is favorablyin the range of 10 to 70 weight %, more favorably 20 to 60 weight %. Inaddition, when the above aqueous solution polymerization is carried out,solvents other than water may be jointly used if necessary, and the kindof the solvents as jointly used is not especially limited.

Examples of the method of the aqueous solution polymerization include: amethod that involves polymerizing an aqueous monomer solution in adouble-arm type kneader while the resultant hydrogel is pulverized; anda method that involves supplying an aqueous monomer solution into adetermined vessel or onto a moving belt and pulverizing the resultantgel from polymerization with such as a meat chopper.

When the above polymerization is initiated, the following radicalpolymerization initiators, for example, can be used: radicalpolymerization initiators, such as potassium persulfate, ammoniumpersulfate, sodium persulfate, t-butyl hydroperoxide, hydrogen peroxide,and 2,2′-azobis(2-amidinopropane)dihydrochloride; andphotopolymerization initiators such as2-hydroxy-2-methyl-1-phenyl-propane-1-one. Furthermore, redox initiatorsare also available by using reductants together to promote decompositionof the above polymerization initiator and combining both with eachother. Examples of the above reductants include: (bi)sulfurous acid (orits salts) such as sodium sulfite and sodium hydrogensulfite; L-ascorbicacid (or its salts); reducible metals (or their salts) such as ferroussalts; and amines. However, the reductants are not especially limitedthereto.

The amount of these polymerization initiators as used is in the range ofusually 0.001 to 2 mol %, preferably 0.01 to 0.1 mol %. In the casewhere the amount of these polymerization initiators is less than 0.001mol %, there are disadvantages in that the amount of unreacted monomersis increased, and therefore the residual amount of the monomers isincreased in the resultant water-absorbent resin. On the other hand, inthe case where the amount of these polymerization initiators is morethan 2 mol %, there may be disadvantages in that the water-extractablecontent in the resultant polymer is increased.

In addition, the polymerization reaction may be initiated by irradiatingthe reaction system with active energy rays, such as radiations,electron beam, and ultraviolet rays, and further using thepolymerization initiators together. Incidentally, the reactiontemperature is not especially limited in the above polymerizationreaction, but is preferably in the range of 15 to 130° C., morepreferably 20 to 110° C. In addition, the reaction time is notespecially limited either, and may fitly be determined according tofactors such as the respective kinds of the hydrophilic monomers andpolymerization initiators and the reaction temperature.

The above water-absorbent resin may be a self-crosslinking type resinusing no crosslinking agent, but is favorably obtained by copolymerizingor reacting with an internal-crosslinking agent that has two or morepolymerizable unsaturated groups or two or more reactive groups per amolecule.

Examples of these internal-crosslinking agents include:N,N′-methylenebis(meth)acrylamide, (poly)ethylene glycoldi(meth)acrylate, (poly)propylene glycol di(meth)acrylate,trimethylolpropane tri(meth)acrylate, glycerol tri(meth)acrylate,glycerol acrylate methacrylate, ethylene-oxide-modifiedtrimethylolpropane tri(meth)acrylate, pentaerythritolhexa(meth)acrylate, triallyl cyanurate, triallyl isocyanurate, triallylphosphate, triallylamine, poly(meth)allyloxyalkanes, (poly)ethyleneglycol diglycidyl ether, glycerol diglycidyl ether, ethylene glycol,polyethylene glycol, propylene glycol, glycerol, pentaerythritol,ethylenediamine, ethylene carbonate, propylene carbonate, andglycidyl(meth)acrylate.

These internal-crosslinking agents may be used either alone respectivelyor in combinations with each other. In addition, theseinternal-crosslinking agents may be added to the reaction system eitherall at once or divisionally. When at least one kind or two kinds ofinternal-crosslinking agents are used, it is favorable to essentiallyuse a compound having two or more polymerizable unsaturated groups inconsideration of the absorption properties of the resultantwater-absorbent resin.

The amount of the above internal-crosslinking agent as used is in therange of favorably 0.005 to 2 mol %, more favorably 0.02 to 0.5 mol %,still more favorably 0.04 to 0.2 mol %, of the above monomers. In thecase where the amount of the internal-crosslinking agent is less than0.005 mol % and the amount of the internal-crosslinking agent is morethan 2 mol %, the water-absorbent resin having sufficient waterabsorption properties might not be obtained.

When the crosslinking structure is introduced into the internal portionof the water-absorbent resin using the above internal-crosslinkingagent, the internal-crosslinking agent may be added to the reactionsystem before, during or after polymerization of the above monomers, orafter neutralization.

Incidentally, in the above polymerization, the following materials maybe added to the reaction system: various foaming agents, such ascarbonates (or hydrogencarbonates), carbon dioxide, azo compounds, andinert organic solvents; hydrophilic polymers, such as starch-cellulose,their derivatives, polyvinyl alcohol, polyacrylic acid (or its salts),and crosslinked products of polyacrylic acid (or its salts); varioussurfactants; chelating agents; and chain transfer agents such ashypophosphorous acid (or its salts). In addition, inorganic powders mayalso be added thereto.

When the above crosslinked polymer is obtained by the aqueous solutionpolymerization and is a gel, namely, a crosslinked hydrogel polymer, thecrosslinked polymer is dried, if necessary, and usually pulverizedbefore and/or after drying in order to produce a water-absorbent resin.In addition, the drying is carried out at a temperature of usually 60 to250° C., favorably 100 to 220° C., more favorably 120 to 200° C., andthe drying time is in the range of 10 minutes to 12 hours, favorably 20minutes to 6 hours, more favorably 30 minutes to 3 hours.

The water content of the water-absorbent resin usable in the presentinvention is not especially limited, but is favorably in the range of 0to 400 weight %, more favorably 0.2 to 40 weight %, still more favorably0.2 to 10 weight %.

In addition, the water-absorbent resin usable in the present invention,for example, is a pulverized one. The water-absorbent resin, which has aweight-average particle diameter of larger than 1,000 μm when thewater-absorbent resin is a gel obtained by the polymerization reactionbefore drying and pulverization, can be used. However, theweight-average diameter is usually in the range of 10 to 1,000 μm,favorably 100 to 800 μm, more favorably 150 to 700 μm (but not including150 μm), still more favorably 300 to 600 μm (but not including 300 μm),most favorably 400 to 500 μm (but not including 400 μm). Furthermore,the water-absorbent resin favorably contains little fine particle (forexample, not larger than 149 μm), for example, in an amount of not morethan 10 weight %, favorably not more than 5 weight %, particularlyfavorably not more than 3 weight %. The particle shape of thewater-absorbent resin as obtained in the above way, for example, may bespherical, pulverized, or irregular, and is not especially limited.However, those having irregular pulverized shapes as obtained via thepulverization step are preferably used.

In addition, the water-absorbent resin particles (A) as used in thepresent invention are favorably obtained by a process including the stepof crosslinking the surface neighborhood of the water-absorbent resin asobtained by the above method with a specific surface-crosslinking agentwhen the occasion demands. Preferred examples of thesurface-crosslinking agent as used in the present invention include acompound having at least two functional groups reactable with afunctional group in the water-absorbent resin. The functional group inthe water-absorbent resin is favorably an anionic dissociative group,more favorably a carboxyl group.

Examples of these surface-crosslinking agents include: polyhydricalcohol compounds such as ethylene glycol, diethylene glycol, propyleneglycol, triethylene glycol, tetraethylene glycol, polyethylene glycol,1,3-propanediol, dipropylene glycol, 2,2,4-trimethyl-1,3-pentanediol,polypropylene glycol, glycerol, polyglycerol, 2-butene-1,4-diol,1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol,1,2-cyclohexanedimethanol, 1,2-cyclohexanol, trimethylolpropane,diethanolamine, triethanolamine, polyoxypropylene,oxyethylene-oxypropylene block copolymers, pentaerythritol and sorbitol;epoxy compounds such as ethylene glycol diglycidyl ether, polyethylenediglycidyl ether, glycerol polyglycidyl ether, diglycerol polyglycidylether, polyglycerol polyglycidyl ether, propylene glycol diglycidylether, polypropylene glycol diglycidyl ether and glycidol; polyaminecompounds, such as ethylenediamine, diethylenetriamine,triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine andpolyethylenimine, and their inorganic or organic salts (for example,azetidinium salts); polyisocyanate compounds such as 2,4-tolylenediisocyanate and hexamethylene diisocyanate; polyoxazoline compoundssuch as 1,2-ethylenebisoxazoline; alkylene carbonate compounds such as1,3-dioxolan-2-one, 4-methyl-1,3-dioxolan-2-one,4,5-dimethyl-1,3-dioxolan-2-one, 4,4-dimethyl-1,3-dioxolan-2-one,4-ethyl-1,3-dioxolan-2-one, 4-hydroxymethyl-1,3-dioxolan-2-one,1,3-dioxan-2-one, 4-methyl-1,3-dioxan-2-one,4,6-dimethyl-1,3-dioxan-2-one and 1,3-dioxopan-2-one; haloepoxycompounds, such as epichlorohydrin, epibromohydrin andα-methylepichlorohydrin, and their polyamine adducts (for example,Kymene produced by Hercules: registered trademark); silane couplingagents such as γ-glycidoxypropyltrimethoxysilane andγ-aminopropyltriethoxysilane; and polyvalent metallic compounds such ashydroxides and chlorides of zinc, calcium, magnesium, aluminum, iron andzirconium. In addition, examples of the usable surface-crosslinkingagent are disclosed in JP-A-180233/1983, JP-A-16903/1986,JP-A-189103/1984, JP-A-117393/1977, JP-A-136588/1976, JP-A-257235/1986,JP-A-7745/1987, JP-A-211305/1986, JP-A-252212/1986, JP-A-264006/1986, DE4020780, WO 99/42494, WO 99/43720, WO 00/31153, and JP-A-197818/2000.These can be used either alone respectively or in combinations with eachother.

In addition, the amount of these surface-crosslinking agents as used isin the range of about 0.001 to 10 parts by weight, favorably 0.01 to 5parts by weight, relative to 100 parts by weight of the water-absorbentresin particles. In the case where the amount is more than 10 parts byweight, there are disadvantages in that not only it is uneconomicalbecause the suitable properties are not caused but also the residualamount of the surface-crosslinking agent is increased. Furthermore, inthe case where the amount of the surface-crosslinking agent as used isless than 0.001 part by weight, there are disadvantages in that theabsorption capacity under a load is not improved enough.

In addition, inorganic acids and organic acids may also be used in orderto further accelerate the reaction of the surface-crosslinking agent andto further improve the absorption properties. Examples of theseinorganic acids and organic acids include sulfuric acid, phosphoricacid, hydrochloric acid, citric acid, glyoxylic acid, glycolic acid,glycerophosphoric acid, glutaric acid, cinnamic acid, succinic acid,acetic acid, tartaric acid, lactic acid, pyruvic acid, fumaric acid,propionic acid, 3-hydroxypropionic acid, malonic acid, butyric acid,isobutyric acid, imidionoacetic acid, malic acid, isethionic acid,citraconic acid, adipic acid, itaconic acid, crotonic acid, oxalic acid,salicylic acid, gallic acid, sorbic acid, gluconic acid, andp-toluenesulfonic acid. The amount of these as used is varied accordingto pH of the water-absorbent resin, but it is favorably in the range of0 to 10 parts by weight, more favorably 0.1 to 5 parts by weight,relative to 100 parts by weight of the water-absorbent resin.

When the water-absorbent resin and the surface-crosslinking agent areblended together in the present invention, water is favorably used as asolvent. The amount of the water as used depends upon the kind orparticle diameter of the water-absorbent resin, but is favorably morethan 0 and not more than 20 parts by weight, more favorably in the rangeof 0.5 to 10 parts by weight, still more favorably 0.5 to 5 parts byweight, relative to 100 parts by weight of the solid content of thewater-absorbent resin.

In addition, when the water-absorbent resin and the surface-crosslinkingagent are blended together, a hydrophilic organic solvent may also beused as the solvent if necessary. Examples of the hydrophilic organicsolvent include: lower alcohols, such as methyl alcohol, ethyl alcohol,n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol,and t-butyl alcohol; ketones such as acetone; ethers, such as dioxane,tetrahydrofuran, and alkoxypolyethylene glycol; amides such asN,N-dimethylformamide; and sulfoxides such as dimethyl sulfoxide. Theamount of the hydrophilic organic solvent as used depends upon the kindor particle diameter of the water-absorbent resin, but it is favorablynot more than 20 parts by weight, more favorably not more than 10 partsby weight, still more favorably not more than 5 parts by weight,relative to 100 parts by weight of the solid content of thewater-absorbent resin.

Then, when the water-absorbent resin and the surface-crosslinking agentare blended together, for example, the water-absorbent resin isdispersed in the above hydrophilic organic solvent, and thereafter thesurface-crosslinking agent may be added thereto. However, the followingadding method is favorable: the method comprises the step of directlyspraying or dropping the surface-crosslinking agent to thewater-absorbent resin while being stirred, wherein thesurface-crosslinking agent is dissolved or dispersed in water and/or thehydrophilic organic solvent when the occasion demands. In addition, whenwater is used for the blending, a water-insoluble inorganic fineparticle powder or a surfactant may be allowed to coexist. Examples ofthe surfactant and water-insoluble inorganic fine particle powder asused are described in U.S. Pat. No. 5,164,459, EP 827753, EP 349240, andEP 761241.

The blending apparatus, which is used when the water-absorbent resin andthe surface-crosslinking agent are blended together, has favorably agreat blending force in order to blend both materials uniformly andsurely. Examples thereof favorably include cylinder type blenders,double-wall cone type blenders, V-character-shaped blenders, ribbon typeblenders, screw type blenders, fluidized-furnace rotary disk typeblenders, gas current type blenders, double-arm type kneaders, internalblenders, pulverizing type kneaders, rotary blenders, screw typeextruders.

After the water-absorbent resin and the surface-crosslinking agent areblended together, the heat treatment and/or photo-irradiation treatmentof the resultant mixture is carried out. Accordingly, the neighboringsurface of the water-absorbent resin is crosslinked, and the AAP, FRUP,and SFC are favorably adjusted to the above range. When the heattreatment is carried out in the present invention, the treatment time isfavorably in the range of 1 to 180 minutes, more favorably 3 to 120minutes, still more favorably 5 to 100 minutes. The treatmenttemperature is favorably in the range of 60 to 250° C., more favorably100 to 210° C., still more favorably 120 to 200° C. In the case wherethe treatment temperature is lower than 60° C., not only the lowering ofthe productivity is caused because it takes much time to carry out theheat treatment, but also the aimed water-absorbent resin particles (A)may not be obtained because the uniform crosslinking is not performed.In addition, in the case where the treatment temperature is higher than250° C., the resultant water-absorbent resin is damaged and thereforethere are cases where the water-absorbent resin excellent in absorptioncapacity cannot be obtained.

The above heat treatment can be carried out with a conventional dryer orfurnace. Examples of the dryer include channel type blending dryers,rotary dryers, disk dryers, fluidized-bed dryers, gas-stream typedryers, and infrared dryers. When the photo-irradiation treatment iscarried out instead of the heat treatment in the present invention, theirradiation with ultraviolet ray is favorably carried out. In addition,photopolymerization initiators can be used.

The water content of the water-absorbent resin particles (A) usable inthe present invention is not especially limited, but it is favorably inthe range of 0 to 400 weight %, more favorably 0.01 to 40 weight %,still more favorably 0.1 to 10 weight %.

In addition, particles having a weight-average particle diameter oflarger than 1,000 μm can also be used as the water-absorbent resinparticles (A) usable in the present invention. However, theweight-average particle diameter is generally in the range of 10 to1,000 μm, favorably 100 to 800 μm, more favorably 150 to 750 μm, stillmore favorably 300 to 650 μm (but excluding 300 μm), most favorably 400to 600 μm (but excluding 400 μm). Furthermore, it is favorable that theamount of fine particles (for example, not larger than 149 μm) in thewater-absorbent resin particles (A) is little. For example, the amountis favorably not more than 10 weight %, more favorably not more than 5weight %, still more favorably not more than 3 weight %.

In addition, particles having a bulk density of less than 0.4 g/ml canalso be used as the water-absorbent resin particles (A) usable in thepresent invention. The bulk density is favorably not less than 0.4 g/ml,more favorably not less than 0.5 g/ml (the measurement method for thebulk density is described in EP 1029886). In the case where the bulkdensity is not more than 0.4 g/ml, the water-absorbent resin particles(A) are damaged by a process and therefore the properties thereof may beworse.

The water-absorbent resin particles (A) as obtained in the above wayfavorably have the above AAP, FRUP, SFC, average particle diameter, bulkdensity, water extractable content, structure, shape, and water content,but the water-absorbent resin particles (A) according to the presentinvention can be obtained by other methods.

—Cationic Polymer Compound (B)—

Hereinafter, the cationic polymer compound (B), which is blended withthe water-absorbent resin particles (A), is explained in the following.

The cationic polymer compound (B) usable in the present invention has awater solubility of 100 to 10 weight %, favorably 100 to 20 weight %,more favorably 100 to 30 weight %. In the case where the watersolubility is less than 10 weight %, the shape-maintaining property orBBS of the swollen water-absorbing agent aggregate, which is onecharacteristic of the water-absorbing agent in the present invention,may be lowered, or this effect may not be maintained for a long time inaddition. Incidentally, the water solubility is obtained by measurementaccording to the following method.

When the cationic polymer compound (B) and the water-absorbent resinparticles (A) are blended together in the present invention, thecationic polymer compound (B) is crosslinked in order that the watersolubility will be favorably adjusted in the range of 100 to 10 weight%, more favorably 100 to 20 weight %, still more favorably 100 to 30weight %. In this case, the cationic polymer compound (B) is favorablyobtained by a process including the step of crosslinking a cationicpolymer with a crosslinking agent. The amount of the crosslinking agentas used is favorably in the range of 0.01 to 10 weight % relative to thecationic polymer (namely, in the range of 0.01 to 10 parts by weightrelative to 100 parts by weight of the cationic polymer), more favorably0.05 to 7.5 weight %, still more favorably 0.1 to 5 weight %. In thecase where the amount is less than 0.01 weight %, the effect of thecrosslinking cannot be obtained. In addition, in the case where theamount is more than 10 weight %, the water solubility of the cationicpolymer compound (B) may be exceedingly lowered.

Especially, when the cationic polymer compound (B) as used is a polymerobtained from an ethylenimine monomer (namely, a polymer obtained frommonomers of which the major proportion comprise an ethylenimine monomer(in the range of not leas than 50 weight %, favorably not leas than 70weight %)), the water solubility is favorably in the range of 70 to 10weight %, more favorably 50 to 10 weight %. In the case where the watersolubility is more than 70%, there are cases where the water-absorbingagent as obtained has insufficient properties and the water absorptionproperties of the water-absorbing agent may be lost with the passage oftime after water is absorbed, because it is not sufficientlycrosslinked. In the case where the water solubility is less than 10weight %, the effect as expected might not be obtained.

When blending with the water-absorbent resin particles (A) which exhibitan AAP of not less than 20 g/g and a FRUP of not more than 800 secondsor the water-absorbent resin particles (A) which exhibit an AAP of notless than 20 g/g and a SFC of not less than 20 (10⁻⁷×cm³×s×g⁻¹), andwhen the water solubility of the cationic polymer compound (B) as usedis less than 10 weight %, the effect as expected might not be obtained.In this case, the cationic polymer compound (B) is, for example,favorably obtained by a process including the step of crosslinking acationic polymer with a crosslinking agent. The cationic polymercompound (B), which is crosslinked with the crosslinking agent of whichthe amount is 0.01 to 10 weight % relative to the cationic polymer, ismore favorable. However, in this case, it is not always necessary thatthe cationic polymer compound (B) is crosslinked.

It is necessary that the amount of the cationic polymer compound (B) asused is in the range of 0.01 to 10 parts by weight, favorably 0.05 to 5parts by weight, more favorably 0.1 to 3 parts by weight, relative to100 parts by weight of water-absorbent resin particles (A). Dependingupon the particle diameters of the water-absorbent resin particles, inthe case where the amount is less than 0.01 part by weight, there arecases where the modification of the water-absorbent resin isinsufficient. In the case where the amount is more than 10 parts byweight, there are cases where the effect cannot be obtained inproportion to the amount as added. In addition, there are alsodisadvantages in economy.

When the above conditions are satisfied, the sinking of the cationicpolymer compound (B) into the water-absorbent resin particles (A) can beprevented, and therefore, the following can be prevented: the waterabsorption properties are lost and the shape-maintaining property andBBS of the swollen water-absorbing agent aggregate are worse with thepassage of time.

The cationic polymer compound (B) is used, for example, in a form ofpowder, aqueous solution, gel-like liquid, or gel-like solid, or in adissolving form in a mixed solvent obtained from water and a hydrophilicorganic solvent such as ethanol, or in a gel form including a mixedsolvent obtained from water and a hydrophilic organic solvent such asethanol. It is not especially limited how the cationic polymer compound(B) is used, but the cationic polymer compound (B) is favorably used ina form of aqueous solution or gel-like liquid.

When the cationic polymer compound (B) is added especially in a form ofaqueous solution, the concentration is not especially limited, but it isfavorably in the range of 1 to 50 weight %, more favorably 2 to 30weight %.

The cationic polymer compound (B), which includes at least one selectedfrom the group consisting of primary amino groups, secondary aminogroups, tertiary amino groups, their salts, and quaternary alkylammoniumsalts, is favorably used. In this case, the salts of the amino groupsare obtained by a neutralization of amino group nitrogen with aninorganic acid or an organic acid, or by a reaction between amino groupnitrogen and an electrophilic reagent. Examples of the inorganic acidusable for the neutralization include: carbonic acid; boric acid;hydrogen acids such as hydrochloric acid and hydrofluoric acid; oxygenacids such as sulfuric acid, sulfurous acid, nitric acid, nitrous acid,phosphoric acid, hypophosphorous acid, phosphorous acid, orthophosphoricacid, metaphosphoric acid, polyphosphoric acids (for example,pyrophosphoric acid), tripolyphosphoric acid, ultraphosphoric acid(acidic metaphosphoric acid), and perchloric acid; salts of the aboveoxygen acids. Examples of the organic acid includeacidic-functional-group-containing compounds, such as carboxylic acids,sulfinic acids, sulfonic acids, phenolic acids, enols (tautomers ofcarbonyl compounds), mercaptans, imides (acid imides), oximes, andsulfonamides. Examples thereof include: hydroxy acids, such as formicacid, acetic acid, propionic acid glycol acid, lactic acid,trichlorolactic acid, glyceric acid, malic acid, tartaric acid, citricacid, tartronic acid, and gallic acid; amino acids such as asparticacid; and p-toluenesulfonic acid. Examples of the usable electrophilicreagent include: alkyl halides, such as methyl iodide, ethyl iodide,2-iodopropane, benzyl iodide, methyl bromide, ethyl bromide,2-bromopropane, benzyl bromide, methyl chloride, ethyl chloride,2-chloropropane, and benzyl chloride; and alkyl sulfates, such asdiethyl sulfate, and dimethyl sulfate. The above inorganic acid, organicacid, and electrophilic reagent are used either alone respectively or incombinations with each other.

Examples of the cationic polymer compound (B) are cationicpolyelectrolytes, such as polyethylenimine, polyamines, modifiedpolyamide amines obtained by a graft reaction of ethylenimine,protonated polyamide amines, condensated products between polyamideamines and epichlorohydrin, condensated products between amines andepichlorohydrin, poly(vinylbenzyldialkylammoniums),poly(diallylalkylammoniums),poly(2-hydroxy-3-methacryloyloxypropyldialkylamines), polyether amines,polyvinylamines, modified polyvinylamines, partially hydrolyzedpoly(N-vinylformamides), partially hydrolyzed poly(N-vinylalkylamides),partially hydrolyzed (N-vinylformamide)-(N-vinylalkylamide) copolymers,polyalkylamines, polyvinylimidazoles, polyvinylpyridines,polyvinylimidazolines, polyvinyltetrahydropyridines,poly(dialkylaminoalkyl vinyl ethers),poly(dialkylaminoalkyl(meth)acrylates), polyallylamines, polyamidines,cationated starch or cellulose, salts thereof, or reaction products ofthe above cationic polyelectrolytes with electrophilic reagents. Thepolyamidines as mentioned herein are polymers having an amidine ring ina molecule, and is favorably obtained by a process including the stepsof: copolymerizing N-vinylformamide and acrylonitrile, and thereaftercarrying out an acid treatment. Examples of the polyamidines includecationic polymers having an amidine structure as described in JapanesePatent No. 2624089, but the polyamidines are not limited thereto. Amongthese, it is favorable that the cationic polymer compound (B) includesat least one member selected from the group consisting of polyamidines,polyvinylamines or salts thereof, and partially hydrolyzedpoly(N-vinylformamides) or salts thereof.

The cationic polymer compound (B) according to the, present inventionfavorably has a weight-average molecular weight of not less than 2,000,more favorably a number-average molecular weight of not less than 2,000,still more favorably a weight-average molecular weight of not less than5,000, yet still more favorably a number-average molecular weight of notless than 5,000, most favorably a weight-average molecular weight of notless than 10,000. In the case where the weight-average molecular weightis less than 2,000, the effect as expected might not be obtained.Incidentally, as to the measurement of the average molecular weight, thenumber-average molecular weight is measured according to viscositymethod, and the weight-average molecular weight is measured according tobalanced sedimentation method. In addition, it is also measured by othermethods such as gel permeation chromatography or static lightscattering.

As to a method for obtaining the crosslinked cationic polymer compound(B), the crosslinking structure can be introduced into the cationicpolymer by conventional methods, such as a method which involvescopolymerizing with other copolymerizable crosslinking agent to producea crosslinked polymer when a corresponding cationic-group-includingmonomer is polymerized, and a method which involves crosslinking acationic polymer with a crosslinking agent having two or more groupsreactable with a functional group (for example, amino group) of thecationic polymer. When the functional group is an amino group, thefollowing conventional compounds can be used: the compounds having twoor more of such as epoxy groups, ketone groups, aldehyde groups, amidegroups, halogenated alkyl groups, isocyanate groups, carboxyl groups,anhydride groups, acid halide groups, amide-bonding portions,ester-bonding portions, or active double bonds per a molecule. Examplesof the above crosslinking agent include: bisepoxy compounds,epichlorohydrin, halohydrins, dihalides such as dibromoethylene,formalin, dialdehyde compounds such as glyoxal, diglycidyl ethers of(poly)ethylene glycols, diglycidyl ethers of (poly)propylene glycols,diglycidyl ethers of dialcohols such as neopentyl alcohol, polyglycidylethers of glycerol, methylenebisacrylamide, and diacrylate compounds,but the crosslinking agent is not limited thereto.

In addition, the cationic polymer compound (B) in the present inventionfavorably has a cation density of not less than 2 mmol/g, more favorablynot less than 4 mmol/g, most favorably not less than 6 mmol/g. In thecase where the cation density is less than 2 mmol/g, theshape-maintaining property or BBS of a water-absorbing agent aggregateafter swelling might be insufficient in a water-absorbing agent obtainedby a process including the step of blending the water-absorbent resinparticles and the cationic polymer compound (B) together.

—Production Process for a Water-absorbing Agent According to the PresentInvention—

The water-absorbing agent, according to the present invention, can beobtained by a process including the step of blending the water-absorbentresin particles (A) and the cationic polymer compound (B) together asobtained in the above way. Hereinafter, the production process forobtaining the water-absorbing agent according to the present inventionis explained.

The production process for a water-absorbing agent according to thepresent invention can be carried out blending the water-absorbent resinparticles (A) and the cationic polymer compound (B) together. When thisblending is carried out, it is not always necessary to heat, and thewater-absorbent resin particles (A) are blended with a solution (forexample, aqueous solution) including the cationic polymer compound (B),or with a gel-like liquid or solid including the cationic polymercompound (B), or with a powdery cationic polymer compound (B).

Accordingly, the aimed water-absorbing agent is obtained. When thesolution including the cationic polymer compound (B), or the gel-likeliquid or solid including the cationic polymer compound (B) is used, anion-bonding layer is formed on the surface of the water-absorbent resinparticles (A) by the blending. When the powdery cationic polymercompound (B) is used, an ion-bonding layer is formed on the surface ofthe water-absorbent resin particles (A) by adding water while or afterthe blending. When the blending is carried out using water or awater-soluble organic solvent, such as aqueous solution, hydrophilicorganic solvent solution, or gel-like liquid or solid, the drying may becarried out by heating after the blending if necessary. The drying isusually carried out at a temperature of favorably 30 to 170° C., morefavorably 50 to 150° C.

In the present invention, various modes can be employed for blending thewater-absorbent resin particles (A) and the cationic polymer compound(B). The blending is carried out by blending the water-absorbent resinparticles (A) with a liquid drop of a solution (for example, aqueoussolution) or a gel-like liquid including the cationic polymer compound(B), or by spraying each liquid to the water-absorbent resin particles(A) in order to blend them. When this blending is carried out, thefollowing apparatuses can be utilized for example: high-speed-stirringblenders, gas-stream type blenders, moving-type blenders, and extruders.The blending can be carried out in the presence of such as organicpowders (for example, cellulose powder) or inorganic powders (forexample, silica fine particle). Furthermore, the water-absorbing agentas obtained may be dried if necessary.

In the present invention, the blending of the water-absorbent resinparticles (A) and the cationic polymer compound (B) can be carried outin any stage such as: before the surface neighborhood of awater-absorbent resin is crosslinked with a special crosslinking agent;when a water-absorbent resin and a crosslinking agent is blendedtogether; while the mixture of a water-absorbent resin and acrosslinking agent is heat-treated; after the mixture of awater-absorbent resin and a crosslinking agent is heat-treated to obtainthe water-absorbent resin particles (A); after the mixture of awater-absorbent resin and a crosslinking agent is heat-treated and theresultant water-absorbent resin particles (A) are cooled; at a stagewhen the particle diameters of the water-absorbent resin particles (A)are adjusted to a specific range with a sieve; or before or after thestage. In addition, the blending may be carried out at two or morestages. Among the stages for the blending, the blending with thecationic polymer compound (B) is favorably carried out at the followingstage: after the mixture of a water-absorbent resin and a crosslinkingagent is heat-treated to obtain the water-absorbent resin particles (A)or after the mixture of a water-absorbent resin and a crosslinking agentis heat-treated and the resultant water-absorbent resin particles (A)are cooled. For example, an effective production process can be formedby blending with the cationic polymer compound (B) in a step of coolingthe water-absorbent resin particles (A) as obtained by heat-treating themixture of the water-absorbent resin and the crosslinking agent. Inaddition, the resultant water-absorbing agent can also be dried byutilizing residual heat at cooling.

In the present invention, the blending of the water-absorbent resinparticles (A) and the cationic polymer compound (B) may be carried outunder any temperature, but it is favorably carried out at 5 to 200° C.,more favorably 25 to 130° C.

In the present invention, the respective temperatures of thewater-absorbent resin particles (A) and the cationic polymer compound(B) when the water-absorbent resin particles (A) and the cationicpolymer compound (B) are blended together are not especially limited,but they are favorably in the range of 5 to 200° C., more favorably 25to 130° C. The respective temperatures of the water-absorbent resinparticles (A) and the cationic polymer compound (B) may be different.

When the water-absorbent resin particles (A) and the cationic polymercompound (B) are blended together, and when the respective temperaturesof the water-absorbent resin particles (A) and the cationic polymercompound (B) are different, the cooling effect may be obtained. Forexample, when the water-absorbent resin particles (A) of 60 to 200° C.and the cationic polymer compound (B) of 0 to 100° C. are blendedtogether, the water-absorbing agent as obtained by the blending caneffectively be cooled.

In the present invention, if necessary, the following materials can beadded even in any stage such as before, while, or after thewater-absorbent resin particles (A) and the cationic polymer compound(B) are blended together: organic powders such as cellulose powder,inorganic powders such as fine particulate silica, antioxidants and/orboric compounds, and surfactants. In addition, examples of the methodfor adding these materials include a method that involves directlyadding them as they are, or a method that involves adding them in a formof aqueous solution. However, it is not especially limited. The amountof these as added is favorably not more than 5 weight %, more favorablynot more than 1 weight % of the water-absorbent resin particles (A).

In addition, in the present invention, the water-absorbing agent may beobtained by blending the water-absorbent resin particles (A) and thecationic polymer compound (B) together and thereafter further blendingthe water-absorbent resin particles (A). The water-absorbent resinparticles (A) as blended further may be or not be the same as of thewater-absorbent resin particles (A) as blended in first time.

In addition, in the present invention, the water-absorbing agent may beobtained by blending the water-absorbent resin particles (A) having aspecific particle range and the cationic polymer compound (B) together,and thereafter further blending the water-absorbent resin particles (A)having a specific particle range. In this production method, thefollowing method is favorable for example: a method that involves thewater-absorbent resin particles (A) having particle diameters of smallerthan 300 μm and the cationic polymer compound (B) together, andthereafter further blending the water-absorbent resin particles (A)having particle diameters of not smaller than 300 μm. However, themethod is not limited thereto.

In the present invention, immediately after the water-absorbent resinparticles (A) and the cationic polymer compound (B) are blendedtogether, the water-absorbing agent as obtained by the blending oftenhas adhesion and difficult handling. This fact is especially remarkablewhen the water-absorbent resin particles (A) and an aqueous solution ofthe cationic polymer compound (B) are blended together. Therefore, thewater-absorbing agent as obtained by the blending is favorably dried.The adhesion is decreased and the handling is improved because of thedrying. The drying time of the water-absorbing agent in the presentinvention is usually in the range of 30 seconds to 60 minutes, favorably1 to 30 minutes. In addition, the drying temperature is not especiallylimited, but it is favorably in the range of 30 to 170° C., morefavorably 50 to 150° C.

In the present invention, the water-absorbent resin particles (A) aregranulated by blending water-absorbent resin particles (A) and thecationic polymer compound (B) together, and the weight-average particlediameter of the water-absorbing agent as obtained in the above way canbe enlarged larger than the average particle diameter of thewater-absorbent resin particles (A). The weight-average particlediameter can be usually enlarged by 30 to 150 μm. In the same way, theratio of the particles having particle diameters of not larger than 149μm can be decreased to not more than 3 weight %. The powder is easilyhandled because of either or both of these, and the liquid permeabilityrepresented by such as SFC can also be improved.

In the present invention, the SFC of the water-absorbing agent asobtained can be increased more than that of the water-absorbent resinparticles (A) by blending water-absorbent resin particles (A) and thecationic polymer compound (B) together.

In the present invention, the particle diameter of the water-absorbingagent is not especially limited, but it is favorable that theweight-average particle diameter in the range of 300 to 600 μm. It ismore favorable that the water-absorbing agent favorably contains littlefine particle (for example, not larger than 149 μm), for example, in anamount of not more than 5 weight %, more favorably not more than 3weight %, particular favorably not more than 1 weight %.

If necessary, the following compounds can be added to thewater-absorbing agent as obtained in the above way: organic powders suchas cellulose powder, inorganic powders such as fine particulate silica,antioxidants and/or boric compounds, and surfactants. Particularly, theliquid permeability can be improved by adding inorganic powders such asfine particulate silica. The amount of these as added is favorably notmore than 5 weight %, more favorably not more than 1 weight % of thewater-absorbing agent.

In addition, a water-absorbing agent may be produced by blending two ormore water-absorbing agents according to the present invention.

In addition, the cationic polymer compound (B) as blended can beisolated by stirring the present invention water-absorbing agent in astrong acidic aqueous solution such as hydrochloric acid. The cationicpolymer compound (B) as isolated in the above away can be identified byconventional analyzing methods, such as nuclear magnetic resonancespectroscopy, infrared spectroscopy, or gel permeation chromatography.

When the water-absorbent resin particles (A) and the cationic polymercompound (B) are substantially ionically bonded in the water-absorbingagent according to the present invention, the following method is onemethod to make sure this. That is to say, when they are substantiallyionically bonded, the water-absorbent resin particles (A) and thecationic polymer compound (B) cannot be separated very much even if thewater-absorbing agent according to the present invention is stirred inpure water. However, the salt exchange is caused by stirring it in thestrong acidic aqueous solution, and the ionic bond between thewater-absorbent resin particles (A) and the cationic polymer compound(B) is dissociated, and these can nearly be isolated. These proceduresare usually carried out by stirring in a liquid of which the weight is200 times as much as the weight of the water-absorbing agent under roomtemperature (20 to 25° C.) in relative humidity of 40 to 60% at theliquid temperature of 20 to 25° C. The stirring time is one hour, andthe stirring is mildly carried out, and hydrochloric acid of 0.1 N isused as the strong acidic aqueous solution. In the present inventionwater-absorbing agent, it is favorably that the water-absorbent resinparticles (A) and the cationic polymer compound (B) are substantiallyionically bonded. Therefore, when the water-absorbing agent according tothe present invention is stirred in pure water by the above-mentionedmethod, the amount of the cationic polymer compound (B) as isolated isfavorably not more than 50 weight %, more is favorably not more than 20weight % of the cationic polymer compound (B) as included in thewater-absorbing agent. When the water-absorbing agent according to thepresent invention is stirred in the strong acidic aqueous solution bythe above-mentioned method, the amount of the cationic polymer compound(B) as isolated is favorably not less than 50 weight %, more isfavorably not less than 80 weight % of the cationic polymer compound (B)as included in the water-absorbing agent.

The present invention water-absorbing agent as obtained by the aboveproduction process is, for example, obtained by blending 100 parts byweight of water-absorbent resin particles (A) and 0.01 to 10 parts byweight of a cationic polymer compound (B) together, wherein the cationicpolymer compound (B) is obtained by a process including the step ofcrosslinking a cationic polymer with a crosslinking agent of which theamount is 0.01 to 10 weight % of the cationic polymer, and wherein thecationic polymer compound (B) has a water solubility of 70 to 10 weight% if the cationic polymer compound (B) is obtained from an ethyleniminemonomer, otherwise the cationic polymer compound (B) has a watersolubility of 100 to 10 weight %.

In addition, the present invention water-absorbing agent as obtained bythe above production process is, for example, obtained by blending 100parts by weight of water-absorbent resin particles (A) and 0.01 to 10parts by weight of a cationic polymer compound (B) together, wherein thewater-absorbent resin particles (A) exhibit an absorption capacity ofnot less than 20 g/g under a load of 4.9 kPa (AAP) and a gel layerliquid permeation rate of not more than 800 seconds under a load (FRUP),and wherein the cationic polymer compound (B) has a water solubility of100 to 10 weight %.

In addition, the present invention water-absorbing agent as obtained bythe above production process is, for example, obtained by blending 100parts by weight of water-absorbent resin particles (A) and 0.01 to 10parts by weight of a cationic polymer compound (B) together, wherein thewater-absorbent resin particles (A) exhibit an absorption capacity ofnot less than 20 g/g under a load of 4.9 kPa (AAP) and a saline flowconductivity of not less than 20 (10⁻⁷×cm³×s×g⁻¹) (SFC), and wherein thecationic polymer compound (B) has a water solubility of 100 to 10 weight%.

In addition, these present invention water-absorbing agents as obtainedby the above production processes favorably have the following values of0.5 hrPT, 16 hrPT, ΔPT, BBS, 16 hrBBS, DBBS, GV, AAP, and SFC.

In addition, the water-absorbing agent according to the presentinvention is also a water-absorbing agent having absorption propertiesas mentioned below.

—Absorption Properties of a Water-absorbing Agent According to thePresent Invention—

The water-absorbing agent according to the present invention, which isobtained in the above way, is a novel water-absorbing agent havingexcellent absorption properties in comparison with conventional ones.

That is to say, the water-absorbing agent according to the presentinvention favorably exhibits a 16 hrPT and/or 0.5 hrPT of not more than12.5 cm, more favorably not more than 11.0 cm, still more favorably notmore than 9.0 cm. In the case where the 16 hrPT and/or 0.5 hrPT is notmore than 12.5 cm, the water-absorbing agent aggregate has moreexcellent shape-maintaining property after it is swollen. In addition,in the case where the 16 hrPT is not more than 12.5 cm, the effect ismaintained for a further long time after water is absorbed. In addition,when the water-absorbing agent is used as a portion of a water-absorbentstructure such as disposable diapers (In general, the width of thewater-absorbent structure is mostly in the range of 11 to 13 cm.) andwhen the 16 hrPT and/or 0.5 hrPT is not more than 12.5 cm, theproperties of the water-absorbent structure, is remarkably improvedbecause the swollen water-absorbing agent in the water-absorbentstructure is neither crushed nor one-sided by pressure such as bodyweight.

The water-absorbing agent according to the present invention favorablyexhibits a ΔPT of not more than 3.5 cm, more favorably not more than 2.0cm. The value of the ΔPT is calculated according to the followingcalculation equation. In the case where the ΔPT is more than 3.5 cm, theshape-maintaining property deterioration of the water-absorbing agentaggregate after it is swollen with the passage of time is too increased.Therefore, when the water-absorbing agent is used for such as awater-absorbent structure for a long time, the properties thereof may bedecreased extremely. In the case where ΔPT is not more than 3.5 cm, theshape-maintaining property can be maintained sufficiently for a longtime. When the water-absorbing agent is used for such as awater-absorbent structure, the properties of the water-absorbentstructure are remarkably improved.

The water-absorbing agent according to the present invention favorablyexhibits a BBS and/or 16 hrBBS of not less than 80 gf, more favorablynot less than 95 gf. These values represent burst strength of gel layeras formed by the water-absorbing agent after it is swollen. In the casewhere the BBS and/or 16 hrBBS is less than 80 gf, the strength of gellayer is decreased rapidly. Therefore, the properties of thewater-absorbent structure may be decreased extremely because the swollenwater-absorbing agent in the water-absorbent structure cannot keep itsshape sufficiently and the water-absorbent structure may be divided. Inthe case where the BBS and/or 16 hrBBS is not less than 80 gf, thewater-absorbing agent can usually obtain sufficient burst strength ofgel layer, and when it is used for such as a water-absorbent structure,the properties of the water-absorbent structure are remarkably improved.In addition, in the case where the 16 hrBBS is not less than 80 gf inparticular, the sufficient burst strength of gel layer can be maintainedfor a long time.

The water-absorbing agent according to the present invention favorablyexhibits a DBBS of not more than 40%, more favorably not more than 25%,still more favorably not more than 10%. In the case where the DBBS ismore than 40%, the deterioration of burst strength of gel layer formedby the water-absorbing agent after it is swollen is too large with thepassage of time. Therefore, when it is used for such as awater-absorbent structure for a long time, the properties thereof may bedecreased extremely. In the case where the DBBS is not more than 40%,the sufficient burst strength of gel layer can usually be maintained fora long time. When the water-absorbing agent is used for such as awater-absorbent structure, the properties of the water-absorbentstructure are remarkably improved.

In order to obtain more excellent water-absorbent structures, the GV ofthe water-absorbing agent is favorably not less than 23 g/g, morefavorably not less than 25 g/g, still more favorably not less than 28g/g, yet still more favorably not less than 31 g/g, most favorably notless than 35 g/g. This is for ensuring the absorption amount of water ofthe water-absorbent structure.

In addition, the AAP of the water-absorbing agent is favorably not lessthan 20 g/g, more favorably not less than 21.5 g/g, still more favorablynot less than 23 g/g, yet still more favorably not less than 24.5 g/g,most favorably not less than 26 g/g in order to more extremely decreasea phenomenon such that the urine as absorbed in the water-absorbentstructure is returned to the surface of the disposable diaper when thepressure is exerted to the water-absorbent structure by body weight.

The SFC of the water-absorbing agent according to the present inventionis favorably not less than 25 (10⁻⁷×cm³×s×g⁻¹), more favorably not lessthan 35 (10⁻⁷×cm³×s×g⁻¹), still more favorably not less than 50(10⁻⁷×cm³×s×g⁻¹), most favorably not less than 100 (10⁻⁷×cm³×s×g⁻¹).When the SFC is adjusted to not less than 25 (10⁻⁷×cm³×s×g⁻¹), thefollowing effects are remarkably improved: when the water-absorbingagent according to the present invention is partially used as awater-absorbent structure of disposable diapers, the liquid permeabilityis improved, and the liquid spreads enough in the water-absorbentstructure, and the absorption amount of water is increased, and the leakof the liquid is prevented.

In addition, the shape of the water-absorbing agent according to thepresent invention is widely selected from shapes such as sheet, gel, orfiber, but the shape is favorably a particulate shape. Thewater-absorbing agent exhibits the similar average particle diameter,particle size, water solubility, and water content as of the abovewater-absorbent resin.

In addition, as is shown in the above way, it is favorable that: thewater-absorbent resin particles (A) and the cationic polymer compound(B) are substantially ionically bonded, or the ionic bond issubstantially formed when they absorb water.

As is shown in the above way, the water-absorbing agent according to thepresent invention

1. favorably exhibits a GV of not less than 23 g/g, and an AAP of notless than 20 g/g, and a 16 hrPT of not more than 12.5 cm.

2. favorably exhibits a GV of not less than 23 g/g, and an AAP of notless than 20 gig, and a 16 hrBBS of not less than 80 gf.

3. favorably exhibits a GV of not less than 23 g/g, and a 16 hrPT of notmore than 12.5 cm, and a ΔPT of not more than 3.5 cm.

4. favorably exhibits a GV of not less than 23 g/g, and a 0.5 hrPT ofnot ore than 12.5 cm, and a ΔPT of not more than 3.5 cm.

5. favorably exhibits a GV of not less than 23 g/g, and a 16 hrBBS ofnot less than 80 gf, and a ΔPT of not more than 3.5 cm.

6. favorably exhibits a GV of not less than 23 g/g, and a BBS of notless than 80 gf, and a ΔPT of not more than 3.5 cm.

7. favorably exhibits a GV of not less than 23 g/g, and a 16 hrPT of notmore than 12.5 cm, and a DBBS of not more than 40%.

8. favorably exhibits a GV of not less than 23 g/g, and a 0.5 hrPT ofnot more than 12.5 cm, and a DBBS of not more than 40%.

9. favorably exhibits a GV of not less than 23 g/g, and a 16 hrBBS ofnot less than 80 gf, and a DBBS of not more than 40%.

10. favorably exhibits a GV of not less than 23 g/g, and a BBS of notless than 80 gf, and a DBBS of not more than 40%.

11. favorably exhibits a GV of not less than 23 g/g, and a SFC of notless than 50 (10⁻⁷×cm³×s×g⁻¹), and a 16 hrBBS of not less than 80 gf.

12. favorably exhibits a GV of not less than 23 g/g, and a SFC of notless than 50 (10⁻⁷×cm³×s×g⁻¹), and a BBS of not less than 80 gf.

13. favorably exhibits a GV of not less than 23 g/g, and a SFC of notless than 50 (10⁻⁷×cm³×s×g⁻¹), and a 16 hrPT of not more than 12.5 cm.

14. favorably exhibits a GV of not less than 23 g/g, and a SFC of notless than 50 (10⁻⁷×cm³×s×g⁻¹), and a 0.5 hrPT of not more than 12.5 cm.

15. favorably exhibits a GV of not less than 23 g/g, and an AAP of notless than 20 g/g, and a 16 hrPT of not more than 12.5 cm or 16 hrBBS ofnot less than 80 gf.

16. favorably exhibits a GV of not less than 23 g/g, and a 16 hrPT or0.5 hrPT of not more than 12.5 cm, and a ΔPT of not more than 3.5 cm.

17. favorably exhibits a GV of not less than 23 g/g, and a 16 hrBBS orBBS of not less than 80 gf, and a ΔPT of not more than 3.5 cm.

18. favorably exhibits a GV of not less than 23 g/g, and a 16 hrPT or0.5 hrPT of not more than 12.5 cm or a 16 hrBBS or BBS of not less than80 gf, and a ΔPT of not more than 3.5 cm.

19. favorably exhibits a GV of not less than 23 g/g, and a DBBS of notmore than 40%, and a 16 hrPT or 0.5 hrPT of not more than 12.5 cm.

20. favorably exhibits a GV of not less than 23 g/g, and a DBBS of notmore than 40%, and a 16 hrBBS or BBS of not less than 80 gf.

21. favorably exhibits a GV of not less than 23 g/g, and a DBBS of notmore than 40%, and a 16 hrPT or 0.5 hrPT of not more than 12.5 cm or a16 hrBBS or BBS of not less than 80 gf.

22. favorably exhibits a GV of not less than 23 g/g, and a SFC of notless than 50 (10⁻⁷×cm³×s×g⁻¹), and a 16 hrPT or 0.5 hrPT of not morethan 12.5 cm.

23. favorably exhibits a GV of not less than 23 g/g, and a SFC of notless than 50 (10⁻⁷×cm³×s×g⁻¹), and a 16 hrBBS or BBS of not less than 80gf.

24. favorably exhibits a GV of not less than 23 g/g, and a SFC of notless than 50 (10⁻⁷×cm³×s×g⁻¹), and a 16 hrPT or 0.5 hrPT of not morethan 12.5 cm or a 16 hrBBS or BBS of not less than 80 gf.

25. favorably comprises water-absorbent resin particles (A) and acationic polymer compound (B), wherein the cationic polymer compound (B)is substantially ionically bonded to the water-absorbent resin particles(A), and wherein the water-absorbing agent exhibits a GV of not lessthan 23 g/g, an AAP of not less than 20 g/g, and a SFC of not less than50 (10⁻⁷×cm³×s×g⁻¹).

The water-absorbing agents as recited in the above 3 to 24 morefavorably exhibit an AAP of not less than 20 g/g, still more favorablythe AAP as shown above.

The water-absorbing agents as recited in the above 1, 2, 3, 4, 5, 6, 7,8, 9, 10, 15, 16, 17, 18, 19, 20, and 21 more favorably exhibit a SFC ofnot less than 25 (10⁻⁷×cm³×s×g⁻¹), still more favorably the SFC as shownabove.

The water-absorbing agents as recited in the above 2, 4, 5, 6, 8, 9, 10,11, 12, 14, 17, 20, 23, and 25 more favorably exhibit a 16 hrPT of notmore than 12.5 cm, still more favorably the 16 hrPT as shown above.

The water-absorbing agents as recited in the above 1, 2, 3, 5, 6, 7, 9,10, 11, 12, 13, 15, 17, 20, 23, and 25 more favorably exhibit a 0.5 hrPTof not more than 12.5 cm, still more favorably the 0.5 hrPT as shownabove.

The water-absorbing agents as recited in the above 1, 2, 7, 8, 9, 10,11, 12, 13, 14, 15, 19, 20, 21, 22, 23, 24, and 25 more favorablyexhibit a ΔPT of not more than 3.5 cm, still more favorably the ΔPT asshown above.

The water-absorbing agents as recited in the above 1, 3, 4, 6, 7, 8, 10,12, 13, 14, 16, 19, 22, and 25 more favorably exhibit a 16 hrBBS of notless than 80 gf, still more favorably the 16 hrBBS as shown above.

The water-absorbing agents as recited in the above 1, 2, 3, 4, 5, 7, 8,9, 11, 12, 13, 14, 15, 16, 19, 22, 23, 24, and 25 more favorably exhibita BBS of not less than 80 gf, still more favorably the BBS as shownabove.

The water-absorbing agents as recited in the above 1, 2, 3, 4, 5, 6, 7,11, 12, 13, 14, 15, 16, 17, 22, 23, 24, and 25 more favorably exhibit aDBBS of not less than 80 gf, still more favorably the DBBS as shownabove.

The water-absorbing agents as recited in the above 1 to 24 morefavorably comprises water-absorbent resin particles (A) and a cationicpolymer compound (B), wherein the cationic polymer compound (B) issubstantially ionically bonded to the water-absorbent resin particles(A).

These more favorable ranges of the AAP, SFC, 16 hrPT, 0.5 hrPT, ΔPT,BBS, 16 hrBBS, and DBBS as shown above are applied to the respectivewater-absorbing agents either alone respectively, still more favorablyin combinations with each other.

Among the above water-absorbing agents, the water-absorbing agents asrecited in the 1, 2, 4, 10, 12, 14, 16, 17, 18, 19, 20, 21, 22, 23, 24,and 25 are still more favorable, and the water-absorbing agents asrecited in the 1, 2, 4, 10, and 25 are yet still more favorable.

For example, the water-absorbing agent as recited in the above 1 has asufficient GV and an excellent AAP, and the shape-maintaining propertyof its swollen water-absorbing agent aggregate is maintained after wateris absorbed even if long time passes. Therefore, when it is used for awater-absorbent structure, the remarkable improvement of the propertiesis caused.

In, addition, for example, the water-absorbing agent as recited in theabove 2 has a sufficient GV and an excellent AAP, and its BBS ismaintained after water is absorbed even if long time passes. Therefore,when it is used for a water-absorbent structure, the remarkableimprovement of the properties is caused.

In addition, for example, the water-absorbing agent as recited in theabove 4 has a sufficient GV, and the shape-maintaining property of itsswollen water-absorbing agent aggregate is excellent after water isabsorbed, and the shape-maintaining property of its swollenwater-absorbing agent aggregate is not worse with the passage of time.Therefore, when it is used for a water-absorbent structure, theremarkable improvement of the properties is caused.

In addition, for example, the water-absorbing agent as recited in theabove 10 has a sufficient GV and an excellent BBS after water isabsorbed, and the BBS is not worse with the passage of time. Therefore,when it is used for a water-absorbent structure, the remarkableimprovement of the properties is caused.

In addition, for example, the water-absorbing agent as recited in theabove 25 comprises the water-absorbent resin particles (A) and thecationic polymer compound (B), and has an especially excellent SFC, asufficient GV, and an excellent AAP among water-absorbing agents inwhich the cationic polymer compound (B) is substantially ionicallybonded to the water-absorbent resin particles (A). Therefore, when it isused for a water-absorbent structure, the remarkable improvement of theproperties is caused.

In this way, for example, the water-absorbing agents as recited in theabove 1 to 25 are novel water-absorbing agents exhibiting excellentabsorption properties that are not conventionally found.

For example, these can be produced by the above production process of awater-absorbing agent. In addition, the shape thereof may be sheet, gel,or fiber, and it is not especially limited. However, the shape isfavorably a particulate shape having the particle diameter range asshown above.

The water-absorbing agent according to the present invention hasexcellent absorption properties when it is used for a water-absorbentstructure. That is to say, when the pressure is exerted to thewater-absorbent structure by body weight, the following phenomenon isremarkably improved: the urine as absorbed in the water-absorbentstructure is returned to the surface of the disposable diaper. Inaddition, when the water-absorbing agent according to the presentinvention is solely used as a water-absorbent structure or combined withmaterials such as cellulose fibers, it is difficult to cause themovement or dropping of the water-absorbing agent. Therefore, the effectis maintained for a long time after water is absorbed. In addition, thewater-absorbing agent also has an excellent shape-maintaining propertyor BBS of a water-absorbing agent aggregate after it is swollen, andthis effect is maintained for a long time. Because thisshape-maintaining property or BBS of the water-absorbing agent aggregateafter swelling is excellent, it is difficult to cause the movement ofthe swollen water-absorbing agent in the water-absorbent structure inpractical use and the properties of the water-absorbent structure can bedisplayed sufficiently when the water-absorbing agent is used as aportion of the water-absorbent structure.

—Production Process for a Water-absorbent Structure According to thePresent Invention and its Absorption Properties—

The water-absorbing agent as obtained by the above production process,for example, can be converted to a water-absorbent structure bycombining with suitable materials, wherein the water-absorbent structureis fitted as an absorption layer of sanitary materials. Hereinafter, thewater-absorbent structure according to the present invention isexplained.

The water-absorbent structure according to the present invention is ashaped composition comprising a water-absorbent resin or awater-absorbing agent, and other material, wherein the water-absorbentresin or water-absorbing agent absorbs blood, body fluid, and urine, andis used for disposable diapers, sanitary napkins, incontinent pads, andmedical pads. Examples of the material as used include cellulose fibers.Examples of the cellulose fibers include: wood pulp fibers such asmechanical pulp, chemical pulp, semichemical pulp, digested pulpobtained from wood; and artificial cellulose fibers such as rayon andacetates. Preferred cellulose fibers are wood pulp fibers. Thesecellulose fibers may partially include synthetic fibers, such aspolyamides and polyesters. When the water-absorbing agent according tothe present invention is used as a portion of a water-absorbentstructure, the weight of the water-absorbing agent in thewater-absorbent structure is favorably not less than 30 weight %, morefavorably not less than 50 weight %, still more favorably not less than70 weight %. In the case where the weight of the water-absorbing agentin the water-absorbent structure is less than 30 weight %, thesufficient effect may not be obtained.

In order to obtain a water-absorbent structure from the water-absorbingagent and cellulose fiber wherein the water-absorbing agent is obtainedin the above way, the following conventional means for obtaining thewater-absorbent structure can fitly be selected for example: a methodwhich involves scattering a water-absorbing agent on paper or matcomprising a cellulose fiber, and interposing them if necessary; and amethod which involves uniformly blending a cellulose fiber and awater-absorbing agent. A method, which involves dry-blending awater-absorbing agent and a cellulose fiber, and thereafter compressingthem, is favorable. This method enables to remarkably prevent thewater-absorbing agent from falling from the cellulose fiber. Thecompression is favorably carried out under heating condition, and thetemperature is, for example, in the range of 50 to 200° C. In addition,in order to obtain the water-absorbent structure, the methods describedin JP-A-509591/1997 and JP-A-290000/1997 are also favorably used,

As to the water-absorbing agent as obtained by the production processaccording to the present invention, the water-absorbing agent fallslittle from a combined counter material such as cellulose fibers evenafter it absorbs water and is swollen, and the swollen water-absorbingagent aggregate has an excellent shape-maintaining property and BBS.Therefore, the water-absorbing agent can be used as awater-absorbing-holding agent for various uses because it has excellentabsorption properties. Examples of this water-absorbing-holding agentare described in the following:

-   (1) Water-absorbing-holding agent for absorbent article-   Disposal diapers, sanitary napkins, incontinent pads, medical pads,    and so on-   (2) Water-holding agent for agricultural, horticultural fields-   Substitute agents for water-soluble starch, soil-improving agents,    water-holding agents, agents for maintaining effects of agricultural    chemicals, and so on-   (3) Water-holding agent for architecture-   Dewfall preventives for interior-wallpaper agents, cement additives,    and so on-   (4) Other-   Release-controlling agents, coolness-holding agents, disposal hand    warmers, dirty-soil-solidifying agents, freshness-keeping agents for    food, ion-exchange column materials, dehydration agents for sludge    or oil, drying agents, humidity-adjusting materials, and so on

In addition, when the water-absorbent structure according to the presentinvention is used for sanitary materials such as disposal diapers,sanitary napkins, incontinent pads, and medical pads, they are favorablyused with comprising (a) a liquid-permeable top sheet as arrangedadjacent to a body of a wearing person, (b) a liquid-impermeable backsheet as arranged adjacent to clothes of the wearing person and far awayfrom the body of the wearing person, and (c) a water-absorbent structureas arranged between the top sheet and the back sheet. Thewater-absorbent structure may comprise two or more layers, or may beused together with such as a pulp layer.

In more favorable composition, the water-absorbing agent in thewater-absorbent structure favorably has a unit weight of 60 to 1,500g/m², more favorably 100 to 1,000 g/m², still more favorably 150 to 500g/m².

In addition, in the present invention, various functions can also begiven to the water-absorbing agent according to the present invention byfurther adding thereto materials such as disinfectants, deodorants,antimicrobial agents, perfumes, various inorganic powders, foamingagents, pigments, dyes, hydrophilic short fibers, manure, oxidants,reductants, water, and salts.

(Effects and Advantages of the Invention):

According to the present invention, is obtained the effect of enablingto provide the production process for a water-absorbing agent, in which,when used as a water-absorbent structure, the following phenomenon isremarkably improved: the urine as absorbed in the water-absorbentstructure is returned to the surface of a disposable diaper; and whenthe water-absorbing agent according to the present invention is solelyused as a water-absorbent structure or used in combination withmaterials such as cellulose fibers, it is difficult to cause themovement and the dropping of the water-absorbing agent; and the effectsmaintain for a long time even after water is absorbed; and it isdifficult to cause the movement of the water-absorbing agent afterswelling in the water-absorbent structure when it is practically used;and the properties of the water-absorbent structure can be displayedsufficiently.

According to the present invention, is obtained the effect of enablingto provide the water-absorbing agent, in which, when used as awater-absorbent structure, the following phenomenon is remarkablyimproved: the urine as absorbed in the water-absorbent structure isreturned to the surface of a disposable diaper; and when thewater-absorbing agent according to the present invention is solely usedas a water-absorbent structure or used in combination with materialssuch as cellulose fibers, it is difficult to cause the movement and thedropping of the water-absorbing agent; and the effects maintain for along time even after water is absorbed; and it is difficult to cause themovement of the water-absorbing agent after swelling in thewater-absorbent structure when it is practically used; and theproperties of the water-absorbent structure can be displayedsufficiently.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, the present invention is more specifically illustrated bythe following examples and comparative examples. However, the presentinvention is not limited to these examples. The simple units “%” and“part(s)” denote “weight %” and “part(s) by weight”, respectively.Incidentally, the various performances of the water-absorbent resinparticles, the cationic polymer compound, and the water-absorbing agent(as obtained by blending the water-absorbent resin particles and thecationic polymer compound together) were measured by the followingmethods. Unless otherwise noted in the following measurement, themeasurement is carried out under room temperature (20 to 25° C.) inrelative humidity of 40 to 60%, and the temperature of apparatuses andliquids as used is adjusted in the range of 20 to 25° C.

(a) Free Swelling Capacity (GV)

To a bag (60 mm×60 mm) made by nonwoven fabric, 0.2 g of water-absorbingagent was uniformly added, and then immersed in a large excess (usually,500 ml) of aqueous sodium chloride solution of 0.9 weight %(physiological saline). The bag was pulled up after 60 minutes, and theweight (W1 (g)) of the bag was measured after draining off for 3 minuteswith a centrifugal separator having centrifugal force as described inthe edana ABSORBENCY II 441.1-99. In addition, the same procedure iscarried out without using the water-absorbing agent, and then the weight(W0 (g)) of the bag was measured. Then, the value obtained bysubtracting W0 from W1 was divided by the weight (g) of thewater-absorbing agent, and the free swelling capacity (GV) wascalculated by subtracting the weight (1 g/g) of the initialwater-absorbing agent from the resultant value.

(b) Absorption Capacity Under a Load of 4.9 kPa (AAP)

0.9 g of water-absorbing agent or water-absorbent resin particle isuniformly spread on a stainless wire net of 400 mesh (mesh size: 38 μm)as attached by fusion to the bottom of a plastic supporting cylinder ofan inner diameter 60 mm, on which a piston and a load are furthermounted in sequence, wherein the piston has an outer diameter only alittle smaller than 60 mm and makes no gap with the wall face of thesupporting cylinder, but is not hindered from moving up and down, andthe total weight of the piston and the load are adjusted to uniformlyapply a load of 50 g/cm² (4.9 kPa) to the water-absorbing agent orwater-absorbent resin particle. Then, the weight (Wa) of the resultantset of measurement apparatus is measured. A glass filter of 90 mm ismounted inside a Petri dish having a diameter of 150 mm, and a 0.9weight % aqueous sodium chloride solution (physiological saline) isadded up to the same level as the surface of the glass filter, on whicha filter paper having a diameter of 90 mm is then mounted such that itsentire surface will be wetted, and the excessive liquid is removed. Theabove set of measurement apparatus is mounted on the above wet filterpaper, thereby allowing the water-absorbing agent or water-absorbentresin particle to absorb the liquid under a load. After 1 hour, the setof measurement apparatus is lifted, and its weight (Wb) is measuredagain. The absorption capacity under a load of 4.9 kPa was determined bysubtracting Wa from Wb and by dividing the resultant value by the weight(0.9 g) of the water-absorbing agent or water-absorbent resin particle.In the present invention, the absorption capacity under a load of 4.9kPa is abbreviated to AAP.

(c) Water Solubility

In a beaker of 1,000 ml, 0.01 g of cationic polymer compound is weighedout, and then 500 ml of hydrochloric acid of 0.1 mol/l is added thereto.After they are stirred for an hour, the resultant mixed solution isfiltered with filter paper, and 20 ml of the filtrate is added to abeaker of 50 ml. A few drops of aqueous Toluidine Blue indicatorsolution (produced by Wako Pure Chemicals Co., Ltd.) as an indicator areadded to the beaker. Then, a standard potassium polyvinyl sulfatesolution of 1/400 (mol/l) (produced by Wako Pure Chemicals Co., Ltd.) isslowly dropped, when the point at which the color of the solution haschanged from blue to reddish violet is regarded as the end point. Whenthe theoretical amine value of the cationic polymer compound, the weightof the cationic polymer compound as eluted, and the titration amount ofthe standard potassium polyvinyl sulfate solution until the end pointare regarded as Nc (eq/g), Wc (g), and V (ml), respectively, Wc iscalculated from the following equation:Wc (g)=(1/Nc)×(1/400)×V×500/(20×1000)The wafer solubility (weight %) is calculated from the followingequation:Water solubility (weight %)=Wc/0.01×100

(d) Gel Deformation Under a Load (16 hr Pressure Test)

The procedure as described below is carried out in a room having roomtemperature (20 to 25° C.) and relative humidity of 40 to 60%. On apolypropylene round-dish-like (Petri-dish-like) receptacle 1 having adiameter of 6.0 cm and an edge height of 1.3 cm as described in FIG. 2,1.5 g of water-absorbing agent is uniformly spread. Down to thereceptacle, 30 g of aqueous sodium chloride solution of 0.9 weight %(physiological saline) is added for 30 seconds to swell thewater-absorbing agent. Within 30 seconds after the physiological salineis added, a polypropylene round cover 3 having a diameter of 7.3 cm anda weight of 10.5 g is mounted in order to perfectly coverthe-round-dish-like receptacle 1 including the water-absorbing agent andthe physiological saline, and 459 g of a weight 4 is further mountedthereon.

After being left still for 30 minutes under room temperature in thisstate, the receptacle is turned upside down, and the resultant swollenwater-absorbing agent aggregate 2 (about 31.5 g of swollen gelaggregate) is taken out from the receptacle while the shape of theaggregate 2 in the receptacle is substantially kept. Next, as isdescribed in FIG. 3, this swollen water-absorbing agent aggregate 2(usually, columnar swollen gel aggregate having a diameter of about 6 to8 cm and a height of about 1 to 1.5 cm) is added to a sealable plasticbag 5 having a size of: length 17 cm×width 12 cm×thickness 0.004 cm(Unipack F-4 produced by Seisan Nippon Co., Ltd.) so that the aggregate2 can be arranged in the center of the bag while the shape of theaggregate 2 in the receptacle is substantially kept. Then, about 90%portion of the seal is closed, and the bag is left still under roomtemperature for 16 hours.

After the bag is left still, as is described in FIG. 4, a columnarweight 6 having a base area of 70.8 cm² and a weight of 3,485 g ismounted onto the plastic bag 5 including the swollen water-absorbingagent aggregate, so that the center of the swollen water-absorbing agentaggregate 2 can just overlap with the center of the columnar weight 6when they are looked at from top. Then, they are pressurized by theweight of the weight 6 for one minute. The weight is removed after oneminute, and the deformed gel resultant from the applied pressure isfurther left still for 30 seconds. After 30 seconds, as is described inFIG. 5, the straight distance 8 between two points, where the straightdistance will be the longest from one arbitrary end to the otherarbitrary end in the deformed swollen water-absorbing agent aggregate 7,is measured, and the resultant length is regarded as the gel deformationunder a load (16 hr PT). The unit of the gel deformation under a load isexpressed by cm. In addition, the gel deformation under a load isabbreviated to 16 hrPT.

(e) Gel Layer Liquid Permeation Rate Under a Load (FRUP)

A glass column equipped with a cock (“Biocolumn CF-30K”, code ofcatalogue published by Iuchi Seiei Dou Co., Ltd.: 22-635-07, lowerfilter: #G2, inner diameter: 1 inch, and length: 400 mm) was packed with0.5 g of water-absorbent resin particles, and the water-absorbent resinparticles were equilibrium-swollen by an excess of physiological saline(for about 30 minutes to one hour). Next, as is shown in FIG. 1, afterswollen water-absorbent resin particles A were sufficiently sedimented,a round plate C on which a weight B could be mounted and a pressurizingrod D under which a pressurizing plate I having a glass filter wasarranged (The pressurizing plate I has the following size: thickness of10 mm and diameter of 1 inch, and is equipped with the glass filter(#G0) in the lowest portion, and a disc thereon has a structure suchthat there are 84 bored holes having a diameter of 1 mm at regularintervals of 2 mm. The pressurizing plate I having the glass filter canfreely be moved up and down in the glass column K, and has a structuresuch that the physiological saline can pass from the upper portion ofthe pressurizing plate I through the glass filter H.) are mounted on theswollen water-absorbent resin particles A while air is discharged. As isdescribed in FIG. 1, the weight B was further mounted in order touniformly apply a load of 24.5 g/cm² (2.4 kPa) to the swollenwater-absorbent resin particles A. As is described in FIG. 1, the liquidsurface was adjusted to a liquid height of 200 mm and the cock wasopened, and then the time when the physiological saline J passed betweentwo standard lines L (liquid surface having a liquid height of 150 mm)and M (liquid surface having a liquid height of 100 mm) as described inFIG. 1 (liquid amount: 25 ml according to measurement) was measured.Then, the average of the resultant three determinations was regarded asthe gel layer liquid permeation rate (second) under a load (FRUP).Incidentally, when the present apparatus was used without thewater-absorbent resin particles, the value as measured was 10 seconds.In the present invention, the gel layer liquid permeation rate under aload is abbreviated to FRUP.

(f) Average Particle Diameter and Particle Size

The particle distribution was obtained by classifying with JIS standardsieves (850 μm, 600 μm, 300 μm, 150 μm, and 45 μm), and was plotted onlogarithmic probability paper to determine the weight-average particlediameter D50.

(g) Extractable Content

In 1,000 ml of deionized water, 0.5 g of water-absorbent resin orwater-absorbent resin particles was dispersed, and they were stirred for16 hours, and thereafter the resultant swollen gel was filtrated withfilter paper. Then, the extractable content (weight %, relative to thewater-absorbent resin particles) as eluted from the water-solublepolymer, namely the water-absorbent resin particles in the resultantfiltrate was measured with colloidal titration, in which an aqueousToluidine Blue indicator solution (produced by Wako Pure Chemicals Co.,Ltd.) was used as an indicator, and a predetermined amount (usually 10ml) of methylglycol chitosan solution of 0.005 mol/l (produced by WakoPure Chemicals Co., Ltd.) was titrated with a standard potassiumpolyvinyl sulfate solution of 1/400 (mol/l) (produced by Wako PureChemicals Co., Ltd.).

(h) Water Content

1.0 g of water-absorbent resin or water-absorbent resin particles wasplaced on an aluminum cup, and it was dried in an airless dryer of 180°C. for 3 hours. Then, the water content was measured according to theweight decrease by the drying.

(i) Cation Density

In a beaker of 1,000 ml, 0.01 g of cationic polymer compound is weighedout, and then 500 ml of hydrochloric acid of 0.1 mol/l is added thereto.After they are stirred for 10 minutes, 20 ml of this solution was addedto a beaker of 50 ml. To the beaker, a few drops of aqueous ToluidineBlue indicator solution (produced by Wako Pure Chemicals Co., Ltd.) asan indicator are added. Then, a standard potassium polyvinyl sulfatesolution of 1/400 (mol/l) (produced by Wako Pure Chemicals Co., Ltd.) isslowly dropped, when the point at which the color of the solution haschanged from blue to reddish violet is regarded as the end point. Whenthe titration amount of the standard potassium polyvinyl sulfatesolution until the end point is regarded as V (ml), the cation dencityis calculated from the following equation:Cation density (mmol/g)=(V×(1/400))/(0.01×(20/500))

(j) Saline Flow Conductivity (SFC) Test (Refer to JP-A-509591/1997)

The following test was carried out according to the saline flowconductivity (SFC) test as described in JP-A-509591/1997.

An apparatus as described in FIG. 7 was used, and a water-absorbingagent (0.900 g) as uniformly added to a receptacle 40 was swollen inartificial urine for 60 minutes under a load of 0.3 psi (2.07 kPa), andthe gel height of the resultant gel 44 was recorded. Next, under a loadof 0.3 psi. (2.07 kPa), an aqueous sodium chloride solution 33 of 0.69weight % was passed through the swollen gel layer from a tank 31 under aconstant hydrostatic pressure. This SFC test was carried out under roomtemperature (20 to 25° C.). The amount of the liquid passing through thegel layer versus time at twenty seconds' interval is recorded with acomputer and a balance for 10 minutes. The flow rate through the swollengel 44 (mainly among particles thereof), F_(s) (t) is determined in aunit of g/s by dividing the incremental weight (g) by incremental time(s). The time when the constant hydrostatic pressure and the stable flowrate are obtained is regarded as t_(s), and only the data collected fortimes between t_(s) and 10 minutes is used for flow rate calculations.F_(s) (t=0) value, namely the initial flow rate through the gel layer iscalculated from the flow rate between t_(s) and 10 minutes. F_(s) (t=0)is calculated by extrapolating the results of a least-squares fit ofF_(s) (t) versus time to t=0.

$\begin{matrix}{{{Saline}\mspace{14mu}{flow}\mspace{14mu}{conductivity}} = {\left( {{F_{s}\left( {t = 0} \right)} \times L_{0}} \right)/\left( {\rho \times A \times \Delta\; P} \right)}} \\{= {{\left( {{F_{s}\left( {t = 0} \right)} \times L_{0}} \right)/139}\text{,}506}}\end{matrix}$

where:

F_(s) (t=0): flow rate in g/sec;

L₀: initial thickness of gel layer in cm;

ρ: density of NaCl solution (1.003 g/cm³);

A: area of the upper side of gel layer in the cell 41 (28.27 cm²);

ΔP: hydrostatic pressure applied to gel layer (4,920 dyne/cm²); and

the unit of the saline flow conductivity is: 10⁻⁷×cm³×s×g⁻¹.

In the apparatus as described in FIG. 7, a glass tube 32 is insertedinto the tank 31, and the lower end of the glass tube 32 was arranged sothat the aqueous sodium chloride solution 33 of 0.69 weight % could bemaintained in a height of 5 cm from the bottom of the swollen gel 44 ina cell 41. The aqueous sodium chloride solution 33 of 0.69 weight % inthe tank 31 was supplied to the cell 41 through a L-tube 34 having acock. A receptacle 48 to collect the passed liquid was arranged underthe cell 41, and the collecting receptacle 48 was arranged on a balance49. The inner diameter of the cell 41 was 6 cm, and a No. 400 stainlesswire mesh 42 (mesh opening size of 38 μm) was arranged on the bottomthereof Sufficient holes 47 where the liquid passed was arranged at thelower portion of a piston 46, and the bottom portion was equipped with apermeable glass filter 45 so that the water-absorbing agent or itsswollen gel would not enter the holes 47. The cell 41 was placed on astand to put on the cell. The face coming in contact with the cell wasarranged on a stainless wire mesh 43 that did not inhibit liquidpermeation.

The artificial urine (1) as used was obtained by adding: 0.25 g calciumchloride dihydrate; 2.0 g of potassium chloride; 0.50 g of magnesiumchloride hexahydrate; 2.0 g of sodium sulfate; 0.85 g of ammoniumdihydrogen phosphate; 0.15 g of diammonium hydrogen phosphate; and994.25 g of pure water.

(k) Ball Burst Strength (BBS) Test (Refer to JP-A-509591/1997)

The following test was carried out according to the ball burst strength(BBS) test as described in JP-A-509591/1997.

This test is for measuring the ball burst strength (BBS) of awater-absorbent agent at wet (swollen) state. The BBS of thewater-absorbent agent is the force (peak load, in grams) required torupture a water-absorbent agent gel layer that is swollen in theartificial urine (1) under procedures specified in this test method. TheBBS of the water-absorbent agent is used for evaluation of the wetintegrity of the water-absorbent agent that is swollen in the artificialurine (1).

(k-1) Sample Preparation Apparatus

A suitable sample preparation apparatus for BBS measurement is describedin FIG. 8. This apparatus comprises an inner-cylinder 270 that is usedto contain a v water-absorbent agent layer 260, a Teflon flat-bottomedtray 240, an inner-cylinder cover plate 220, and a stainless weight 210.The inner-cylinder 270 is bored from a transparent LEXAN rod (or itsequivalent, for example, acryl resin rod) and has an inner diameter of6.00 cm (=28.27 cm²), a wall thickness of about 0.5 cm, and a height ofabout 1.50 cm. An outside-cylinder 230 is bored from a transparent LEXANrod (or its equivalent, for example, acryl resin rod) and has an innerdiameter slightly larger than the outside diameter of the inner-cylinder270, so that the inner-cylinder 270 can exactly fit within theoutside-cylinder 230 and slide freely. The outside-cylinder 230 has awall thickness of about 0.5 cm, and a height of about 1.00 cm. Thebottom of the outside-cylinder 230 is faced with a No. 400 mesh (meshopening size of 38 μm) stainless-steel screen 250 that is biaxiallystretched to tautness prior to attachment. The inner-cylinder coverplate 220 is made of glass plate with a thickness of 0.8 cm and a weightof 500 g. The stainless weight 210 has a weight of 1700 g.

(k-2) Burst Testing Machine

A tensile tester with a burst test load cell (Intelevt-II-STD TensileTester, Thwing Tester, produced by Thwing-Albert Instrument Co.,Pennsylvania) is used for this test.

As to FIG. 9, this apparatus comprises: a circular sample lower clampplaten 280 that is mount on a stationary crosshead 310 provided at thetop of a dual screw instrument; a force sensing load cell 330 equippedwith a polished stainless steel ball-shaped probe 290; a movingcrosshead 320; and an upper clamping platen 300 that is used to clamp asample 260 pneumatically. The lower clamp platen 280 is attached on thestationary crosshead 310. The force sensing load cell 330 is equippedwith the probe 290. Both the lower clamp platen 280 and the upper clampplaten 300 have a diameter of 115 mm, a thickness of 2.9 mm, and acircular opening 18.65 mm in diameter. The polished stainless steelball-shaped probe 290 has a diameter of 15.84 mm. The moving crosshead320 moves up, and causes the probe 290 to contact and penetrate thesample 260. When the probe 290 penetrates the sample 260, it isconsidered that the test is completed, and the test result data aredisplayed and recorded.

(k-3) Procedure

As to FIG. 8, the inner-cylinder 270 was inserted into theoutside-cylinder 230. To the inner-cylinder 270, 1.4 g aliquot of thewater-absorbent agent was added and dispersed uniformly on the 400 mesh(mesh opening size of 38 μm) stainless screen 250 of the bottom bygently shaking and/or tapping of the assembled cylinders. The assembledcylinders including the water-absorbent agent were transferred to theTeflon flat-bottomed tray 240, and the inner-cylinder cover plate 220was positioned onto the inner-cylinder 270. To the Teflon flat-bottomedtray, 240, 42.0 ml of the artificial urine (1) was added. The artificialurine (1) passed through the stainless screen 250 from the Teflonflat-bottomed tray 240. All of the artificial urine (1) as added wasabsorbed by the water-absorbent agent 260 within 5 minutes. Then, thestainless weight 210 was placed onto the inner-cylinder cover plate 220.After further 25 minutes, the stainless weight 210 and theinner-cylinder cover plate 220 were removed. Consequently, thepredetermined layer 260 of the swollen water-absorbent agent for the BBSmeasurement has been prepared. The inner-cylinder 270 including thewater-absorbent agent gel layer 260 was immediately transferred to theburst testing machine for the BBS test.

As to FIG. 9, the inner-cylinder 270 including the water-absorbent agentgel layer 260 was positioned on the lower clamp platen 280 and was fixedpneumatically with the upper clamping platen 300. With a breaksensitivity of 10.00 g and a test speed of 5.00 inch/minutes, the testwas initiated by pressing a test switch. The moving crosshead 320 movedup, and the polished stainless steel ball-shaped probe 290 penetratedthe water-absorbent agent gel layer 260. After a sample burst wasrecorded, the moving crosshead 320 returned to a start position. The BBSis expressed as peak load grams. The average of three determinationsshould be reported. The unit of the BBS is expressed as gf. The ballburst strength is abbreviated to BBS.

(l) 16 Hours' Ball Burst Strength Test (16 hrBBS)

The same measurement method as of the above ball burst strength (BBS)test is carried out. In the above procedure (k-3), the stainless weight210 and the inner-cylinder cover plate 220 were removed after 25 minutesfrom the end of the addition of the artificial urine (1), but thepresent measurement was carried out changing this 25 minutes to 16hours. The 16 hours' ball burst strength is abbreviated to 16 hrBBS.

(m) Gel Deformation Under a Short-time Load (0.5 hr Pressure Test)

The same measurement was carried out except that: still leaving for 16hours under room temperature is changed to still leaving for 30 minutesunder room temperature in the measurement method of the above (d) geldeformation under a load. The unit of the gel deformation under ashort-time load is expressed as cm. In the present invention, the geldeformation under a short-time load is abbreviated to 0.5 hrPT.

(n) Gel Deformation Deterioration Under a Load with the Passage of Time(ΔPT)

The gel deformation deterioration under a load with the passage of time(ΔPT) is expressed by the following equation. This value means extent ofgel deformation deterioration under a load with the passage of time.

Gel  deformation  deterioration under  a  load  with  thepassage  of  time  (Δ PT) = (gel  deformation  under  a  load)−                 (gel  deformation  under  a                 short-time  load)                = (16  hrPT) − (0.5  hrPT)

The gel deformation under a short-time load (0.5 hrPT) is measured bythe above-mentioned method. The unit of the gel deformationdeterioration under a load with the passage of time (ΔPT) is expressedas cm. In addition, the gel deformation deterioration under a load withthe passage of time is abbreviated to ΔPT in the present invention. TheΔPT may be a negative value.

(o) Deterioration of Ball Burst Strength (DBBS)

The deterioration of ball burst strength is expressed by the followingequation. This value means extent of deterioration of ball burststrength.

Deterioration  of  ballburst  strength  (DBBS) = [1 − (16  hours′  ball  burst  strength)/(ball  burst  strength)] × 100                = [1 − (16  hrBBS)/(BBS)] × 100

The deterioration of ball burst strength is abbreviated to DBBS. Theunit of the DBBS is expressed as %. The DBBS may be a negative value.

Referential Example 1

In a reactor as prepared by lidding a jacketed stainless twin-armkneader of 10 liters in capacity with two sigma-type blades, a reactionliquid was obtained by dissolving 0.08 mol % of polyethylene glycoldiacrylate (average molecular weight: 487) in 5,500 g of aqueous sodiumacrylate solution having a neutralization ratio of 71.3 mol % (monomerconcentration: 38 weight %). Next, this reaction liquid was degassedunder an atmosphere of nitrogen for 30 minutes. Continuously, 2.9 g ofammonium persulfate and 0.08 g of L-ascorbic acid were added theretowhile being stirred, and then the reaction was started after about oneminute. Then, the polymerization was carried out at 20 to 90° C. whilethe resultant formed gel was pulverized, and a crosslinked hydrogelpolymer (1) was taken out after 30 minutes from the start of thepolymerization.

The crosslinked hydrogel polymer (1) as obtained was pulverized whereinits diameter was not larger than about 5 mm. This pulverized crosslinkedhydrogel polymer (1) was spread on a metal gauze with 50 mesh (a meshopening size of 300 μm), and hot-wind-dried at 180° C. for 50 minutes.Next, the resultant dry material was pulverized with a roll mill, andfurther classified with JIS vibration sieves having mesh opening sizesof 850 μm and 150 μm, thus obtaining an irregularly pulverizedparticulate water-absorbent resin (1) with an average particle diameterof 450 μm wherein the ratio of resins having particle diameters of notlarger than 149 μm was 3%, a GV of 32 g/g, an uncrosslinkedwater-extractable content of 8 weight % in the water-absorbent resin,and a water content of 5 weight %.

A solution, which included a surface-crosslinking agent comprising 5parts by weight of 1,4-butanediol, 2.5 parts by weight of isopropylalcohol, and 15 parts by weight of water, was added to 500 parts byweight of the water-absorbent resin (1) while being stirred. Theresultant mixture was added to a mortar mixer of 5 L, and stir-treatedfor 30 minutes while being heated in an oil bath of 212° C., thusobtaining water-absorbent resin particles (A-1) which exhibits a GV of25.6 g/g, an AAP of 22.4 g/g, a FRUP of 70 seconds, and a SFC of 101(unit: 10⁻⁷×cm³×s×g⁻¹). The results were summarized in Table 1.

Referential Example 2

In a reactor as prepared by lidding a jacketed stainless twin-armkneader of 10 liters in capacity with two sigma-type blades, a reactionliquid was obtained by dissolving 0.05 mol % of polyethylene glycoldiacrylate (average molecular weight: 487) in 5,500 g of aqueous sodiumacrylate solution having a neutralization ratio of 71.3 mol % (monomerconcentration: 38 weight %). Next, this reaction liquid was degassedunder an atmosphere of nitrogen for 30 minutes. Continuously, 2.9 g ofammonium persulfate and 0.08 g of L-ascorbic acid were added theretowhile being stirred, and then the reaction was started after about oneminute. Then, the polymerization was carried out at 20 to 90° C. whilethe resultant formed gel was pulverized, and a crosslinked hydrogelpolymer (2) was taken out after 30 minutes from the start of thepolymerization.

The crosslinked hydrogel polymer (2) as obtained was pulverized whereinits diameter was not larger than about 5 mm. This pulverized crosslinkedhydrogel polymer (1) was spread on a metal gauze with 50 mesh (a meshopening size of 300 μm), and hot-wind-dried at 180° C. for 50 minutes.Next, the resultant dry material was pulverized with a roll mill, andfurther classified with JIS vibration sieves having mesh opening sizesof 850 μm and 150 μm, thus obtaining an irregularly pulverizedparticulate water-absorbent resin (2) with an average particle diameterof 470 μm wherein the ratio of resins having particle diameters of notlarger than 149 μm was 3%, a GV of 36 g/g, an uncrosslinkedwater-extractable content of 10 weight % in the water-absorbent resin,and a water content of 6 weight %.

A solution, which included a surface-crosslinking agent comprising 5parts by weight of 1,4-butanediol, 2.5 parts by weight of isopropylalcohol, and 15 parts by weight of water, was added to 500 parts byweight of the water-absorbent resin (2) while being stirred. Theresultant mixture was added to a mortar mixer of 5 L, and stir-treatedfor 30 minutes while being heated in an oil bath of 212° C., thusobtaining water-absorbent resin particles (A-2) which exhibited a GV of29.2 g/g, an AAP of 25.1 g/g, a FRUP of 220 seconds, and a SFC of 40(unit: 10⁻⁷×cm³×s×g⁻¹). The results were summarized in Table 1.

Referential Example 3

To 100 parts of 10% aqueous solution of polyallylamine (commercial name:PAA-10C, weight-average molecular weight: about 10,000, produced byNitto Bouseki Co., Ltd.), 0.25 part of ethylene glycol diglycidyl ether(commercial name: Denacol EX810, produced by Nagase Kasei Kogyo Co.,Ltd.) as a crosslinking agent was added while being stirred, and theywere also stirred for one minute after they were blended. This was leftstill at 60° C. for one hour, thus obtaining an aqueous solution of acationic polymer compound (B-1). The cationic polymer compound (B-1) hada water solubility of 97% and a cation density of 17 mmol/g.

Referential Example 4

To 100 parts of 10% aqueous solution of polyethylenimine (number-averagemolecular weight: about 70,000, produced by Nippon Shokubai Co., Ltd.,cation density: 23 mmol/g), 0.5 part of ethylene glycol diglycidyl ether(commercial name: Denacol EX810, produced by Nagase Kasei Kogyo Co.,Ltd.) as a crosslinking agent was added while being stirred, and theywere also stirred for one minute after they were blended. This was leftstill at 60° C. for one hour, thus obtaining an aqueous solution of acationic polymer compound (B-2). The cationic polymer compound (B-2) hada water solubility of 38% and a cation density of 22 mmol/g.

Referential Example 5

To a beaker of 1,000 ml, 350 g of N-vinylformamide and 1,390 g of purewater were added, and this resultant reaction liquid was degassed underan atmosphere of nitrogen for 30 minutes. Continuously, 1.48 g of V-50(Wako Pure Chemicals Co., Ltd.) was added to the reaction liquid whilebeing stirred, and the resultant mixture was heated at 65° C. Then, thereaction was started after about one minute. The resultant polymer wassedimented in ethanol after 16 hours and thereafter dried, thusobtaining poly(N-vinylformamide).

The poly(N-vinylformamide) as obtained in the above way was converted toits aqueous solution of 5 weight %, and 0.5 equivalent of sodiumhydroxide relative to the weight of the polymer was added thereto. Then,the reaction was carried out at 75° C. for 2 hours, thus obtaining anaqueous solution of a cationic polymer compound (B-3) that was apartially hydrolyzed poly(N-vinylformamide). The cationic polymercompound (B-3) had a water solubility of 99% and a cation density of 6mmol/g.

In addition, the poly(N-vinylformamide) as obtained was converted to itsaqueous solution of 5 weight %, and 1.5 equivalent of sodium hydroxiderelative to the weight of the polymer was added thereto. Then, thereaction was carried out at 75° C. for 4 hours, thus obtaining anaqueous solution of polyvinylamine as hydrolyzed poly(N-vinylformamide).

Referential Example 6

To 100 parts of 10% aqueous solution of the polyvinylamine as obtainedin Referential Example 5, 0.05 part of ethylene glycol diglycidyl ether(commercial name: Denacol EX810, produced by Nagase Kasei Kogyo Co.,Ltd.) as a crosslinking agent was added while being stirred, and theywere also stirred for one minute after they were blended. This was leftstill at 60° C. for one hour, thus obtaining an aqueous solution of acationic polymer compound (B-4). The cationic polymer compound (B-4) hada water solubility of 97% and a cation density of 12 mmol/g.

Comparative Referential Example 1

Making reference to a production example of a water-absorbent resin andExample 1 as described in JP-A-31362/1993, its tracing test was carriedout in the following procedure:

A crosslinked hydrogel polymer was obtained by polymerizing 4,000 partsof 37% aqueous solution of an acrylic salt monomer comprising 74.95 mol% of sodium acrylate, 25 mol % of acrylic acid, and 0.05 mol % oftrimethylolpropane triacrylate with 2.0 parts of ammonium persulfate and0.08 part of L-ascorbic acid under an atmosphere of nitrogen at 30 to80° C. After the crosslinked hydrogel polymer as obtained was dried in ahot-wind-dryer of 150° C., and pulverized with a hammer mill, andclassified with a metal gauze having 20 mesh (a mesh opening size of 850μm, Tyler standard sieve), thus obtaining a 20-μm-passed material. Thismaterial is named a water-absorbent resin (3). To 100 parts of thewater-absorbent resin (3), 0.5 part of glycerin, 2 parts of water, and 2parts of ethyl alcohol were added and blended, and thereafter they wereheat-treated at 210° C. for 10 minutes, thus obtaining water-absorbentresin particles (C-1) of which the surface neighborhood was secondarilycrosslinked. The water-absorbent resin particles (C-1) exhibited a GV of34.1 g/g, an AAP of 8.2 g/g, a FRUP of 2,000 seconds, and a SFC of 2(unit: 10⁻⁷×cm³×s×g⁻¹). The results were summarized in Table 1.

Comparative Referential Example 2

Making reference to Referential Example 4 as described inJP-A-95955/2000, its tracing test was carried out in the followingprocedure:

A stainless reactor of 20 L equipped with a dropping funnel, a stirrer,a thermometer, and a condenser was charged with 10 L of a cyclohexanesolution including 100 g of inorganic particles (commercial name:Aerosil R972, produced by Nippon Aerosil Co., Ltd.), and they werestirred under room temperature. Next, to an aqueous polyethyleniminesolution (as cooled at 0° C. beforehand) comprising 5,636 g of 30%polyethylenimine (commercial name: Epomin P-1000, produced by NipponSholubai Co., Ltd., cation density: 23 mmol/g) and 4,000 g of purewater, 363 g of 50% aqueous solution of ethylene glycol diglycidyl ether(commercial name: Denacol EX810, produced by Nagase Kasei Kogyo Co.,Ltd.) as a crosslinking agent was added while being stirred, thuspreparing an aqueous solution including the crosslinking agent and ahydrophilic polymer. Then, this solution was added to the cyclohexanesolution under room temperature while being stirred. The systemtemperature was gradually raised to 65° C. while being stirred, and thereaction was carried out at 65° C. for 3 hours. Thereafter, the systemtemperature was cooled to room temperature, and the resultant formedspherical hydrogel was filtrated by aspiration, and the resultantspherical hydrogel was dried under reduced pressure at 60° C. for 48hours, thus obtaining a fine water-swellable resin particle having awater content of 15% and a cationic group. This was named a cationicpolymer compound (D-1). The cationic polymer compound (D-1) had a watersolubility of 5%.

Comparative Referential Example 3

Making reference to Referential Example 2 as described inJP-A-3123/1997, its tracing test was carried out in the followingprocedure:

In 5,500 g of aqueous sodium acrylate solution having a neutralizationratio of 75 mol % (monomer concentration: 38 weight %), 7 g oftrimethylolpropane triacrylate and 1 g of polyoxyethylene sorbitanmonostearate were dissolved, and they were degassed under an atmosphereof nitrogen. Thereafter, 2.3 g of potassium persulfate and 0.11 g ofL-ascorbic acid were added thereto to carry out polymerization. When thepolymerization was finished, the crosslinked hydrogel polymer wasfurther pulverized and dried in a hot-wind-dryer of 150° C. until thewater content of the crosslinked hydrogel polymer was not more than 5%.The resultant dried product was pulverized with a roll granulator tocollect a 20-mesh-passed material from a metal gauze. This material hadan average particle diameter of about 390 μm, and the ratio of particleshaving particle diameters of smaller than 106 μm was 5 weight %. To 100parts by weight of the 20-mesh-passed material, an aqueous liquidcomprising 0.5 part of glycerin, 3 parts of water, and 0.75 part ofisopropyl alcohol was added to blend them, and the resultant mixture washeat-treated at 200° C. for 33 minutes, thus obtaining water-absorbentresin particles (C-2) having a weak acidic group. The water-absorbentresin particles (C-2) exhibited a GV of 28.2 g/g, an AAP of 21.3 g/g, aFRUP of 1,214 seconds, and a SFC of 10 (unit: 10⁻⁷ cm³×s×g⁻¹). Theresults were summarized in Table 1.

EXAMPLE 1

To 100 parts of the water-absorbent resin particles (A-1) as obtained inReferential Example 1, 10 parts of 10% aqueous solution of the cationicpolymer compound (B-1) as obtained in Referential Example 3 was added toblend them, and they were heat-dried at 90° C. for 20 minutes.Thereafter, the resultant mixture was classified with a sieve having amesh opening size of 850 μm, thus obtaining particles of not larger than850 μm. These are named a water-absorbing agent (1). The variousproperties of the water-absorbing agent (1) as obtained are listed inTables 2 and 3.

EXAMPLE 2

To 100 parts of the water-absorbent resin particles (A-1) as obtained inReferential Example 1, 15 parts of 10% aqueous solution of the cationicpolymer compound (B-2) as obtained in Referential Example 4 was added toblend them, and they were heat-dried at 90° C. for 20 minutes.Thereafter, the resultant mixture was classified with a sieve having amesh opening size of 850 μm, thus obtaining particles of not larger than850 μm. These are named a water-absorbing agent (2). The variousproperties of the water-absorbing agent (2) as obtained are listed inTables 2 and 3.

EXAMPLE 3

To 100 parts of the water-absorbent resin particles (A-2) as obtained inReferential Example 2, 5 parts of 10% aqueous solution of the cationicpolymer compound (B-1) as obtained in Referential Example 3 was added toblend them, and they were heat-dried at 120° C. for 20 minutes.Thereafter, the resultant mixture was classified with a sieve having amesh opening size of 850 μm, thus obtaining particles of not larger than850 μm. These are named a water-absorbing agent (3). The variousproperties of the water-absorbing agent (3) as obtained are listed inTables 2 and 3.

EXAMPLE 4

To 100 parts of the water-absorbent resin particles (A-1) as obtained inReferential Example 1, 3 parts of 50% aqueous solution of polyallylaminehydrochloride (PAA-HCl-3L, weight-average molecular weight: about10,000, produced by Nitto Boseki Co., Ltd, and cation density: 11mmol/g) was added to blend them, and they were heat-dried at 90° C. for20 minutes. Thereafter, the resultant mixture was classified with asieve having a mesh opening size of 850 μm, thus obtaining particles ofnot larger than 850 μm. These are named a water-absorbing agent (4). Thevarious properties of the water-absorbing agent (4) as obtained arelisted in Tables 2 and 3.

EXAMPLE 5

To 100 parts of the water-absorbent resin particles (A-2) as obtained inReferential Example 2, 20 parts of 30% aqueous solution ofpolyethylenimine (number average molecular weight: about 70,000,produced by Nippon Shokubai Co., Ltd., and cation density: 23 mmol/g)was added to blend them, and they were heat-dried at 120° C. for 30minutes. Thereafter, the resultant mixture was classified with a sievehaving a mesh opening size of 850 μm, thus obtaining particles of notlarger than 850 μm. To these particles, 1 part of silicon oxide ofsuper-fine particle (produced by Nippon Aerosil Co., Ltd., commercialname: Aerosil 200) was further added to blend them. This is named awater-absorbing agent (5). The various properties of the water-absorbingagent (5) as obtained are listed in Tables 2 and 3.

EXAMPLE 6

To 100 parts of the water-absorbent resin particles (A-1) as obtained inReferential Example 1, 15 parts of 5% aqueous solution of polyamidine(produced by HYMO Co., Ltd., commercial name: Himoloc ZP-700, and cationdensity: 6 mmol/g) was added to blend them, and they were heat-dried at90° C. for 20 minutes. Thereafter, the resultant mixture was classifiedwith a sieve having a mesh opening size of 850 μm, thus obtainingparticles of not larger than 850 μm. These are named a water-absorbingagent (6). The various properties of the water-absorbing agent (6) asobtained are listed in Tables 2 and 3.

EXAMPLE 7

To 100 parts of the water-absorbent resin particles (A-1) as obtained inReferential Example 1, 10 parts of 10% aqueous solution of the cationicpolymer compound (B-3) as obtained in Referential Example 5 was added toblend them, and they were heat-dried at 90° C. for 20 minutes.Thereafter, the resultant mixture was classified with a sieve having amesh opening size of 850 μm, thus obtaining particles of not larger than850 μm. These are named a water-absorbing agent (7). The variousproperties of the water-absorbing agent (7) as obtained are listed inTables 2 and 3.

EXAMPLE 8

To 100 parts of the water-absorbent resin particles (A-1) as obtained inReferential Example 1, 10 parts of 10% aqueous solution of the cationicpolymer compound (B-4) as obtained in Referential Example 5 was added toblend them, and they were heat-dried at 90° C. for 20 minutes.Thereafter, the resultant mixture was classified with a sieve having amesh opening size of 850 μm, thus obtaining particles of not larger than850 μm. These are named a water-absorbing agent (8). The variousproperties of the water-absorbing agent (8) as obtained are listed inTables 2 and 3.

EXAMPLE 9

To 100 parts of the water-absorbent resin particles (A-1) as obtained inReferential Example 1, 10 parts of 5% aqueous solution of polyamidine(produced by HYMO Co., Ltd., commercial name: Himoloc ZP-700, and cationdensity: 6 mmol/g) was added to blend them, and they were heat-dried at90° C. for 20 minutes. Thereafter, the resultant mixture was classifiedwith a sieve having a mesh opening size of 850 μm, thus obtainingparticles of not larger than 850 μm. To these particles, 0.5 part ofsilicon oxide of super-fine particle (produced by Nippon Aerosil Co.,Ltd., commercial name: Aerosil 200) was further added to blend them.This is named a water-absorbing agent (9). The various properties of thewater-absorbing agent (9) as obtained are listed in Tables 2 and 3.

EXAMPLE 10

To 100 parts of the water-absorbent resin particles (A-1) as obtained inReferential Example 1, 5 parts of 10% aqueous solution of partiallyhydrolyzed poly(N-vinylformamide) (produced by BASF, commercial name:CatiofastPR8106, and cation density: 6.1 mmol/g) was added to blendthem, and they were heat-dried at 90° C. for 20 minutes. Thereafter, theresultant mixture was classified with a sieve having a mesh opening sizeof 850 μm, thus obtaining particles of not larger than 850 μm. To theseparticles, 0.5 part of silicon oxide of super-fine particle (produced byNippon Aerosil Co., Ltd., commercial name: Aerosil 200) was furtheradded to blend them. This is named a water-absorbing agent (10). Thevarious properties of the water-absorbing agent (10) as obtained arelisted in Tables 2 and 3.

EXAMPLE 11

To 100 parts of the water-absorbent resin particles (A-1) as obtained inReferential Example 1, 7 parts of 10% aqueous solution of polyamidine(produced by Dia-Nitrix Co., Ltd., commercial name: PVAD-L, and cationdensity: 5.8 mmol/g) was added to blend them, and they were heat-driedat 90° C. for 20 minutes. Thereafter, the resultant mixture wasclassified with a sieve having a mesh opening size of 850 μm, thusobtaining particles of not larger than 850 μm. To these particles, 0.5part of silicon oxide of super-fine particle (produced by Nippon AerosilCo., Ltd., commercial name: Aerosil 200) was further added to blendthem. This is named a water-absorbing agent (11). The various propertiesof the water-absorbing agent (11) as obtained are listed in Tables 2 and3.

Comparative Example 1

The water-absorbent resin particles (A-1) as obtained in ReferentialExample 1 were named a comparative water-absorbing agent (1). Thevarious properties of the comparative water-absorbing agent (1) asobtained are listed in Tables 2 and 3.

Comparative Example 2

To 100 parts of the water-absorbent resin particles (C-1) as obtained inComparative Referential Example 1, 5 parts of 30% aqueous solution ofpolyethylenimine (number-average molecular weight: about 70,000 andproduced by Nippon Shokubai Co., Ltd.) was added, thus obtaining acomparative water-absorbing agent (2). The various properties of thecomparative water-absorbing agent (2) as obtained are listed in Tables 2and 3.

Comparative Example 3

To 100 parts of the water-absorbent resin particles (A-1) as obtained inReferential Example 1, 5 parts of the cationic polymer compound (D-1) asobtained in Comparative Referential Example 2 was added, thus obtaininga comparative water-absorbing agent (3). The various properties of thecomparative water-absorbing agent (3) as obtained are listed in Tables 2and 3.

Comparative Example 4

To 100 parts of the water-absorbent resin particles (C-1) as obtained inComparative Referential Example 1, 10 parts of 30% aqueous solution ofethylenediamine was added, and they were heat-dried at 90° C. for 20minutes. Thereafter, the resultant mixture was classified with a sievehaving a mesh opening size of 850 μm, thus obtaining particles of notlarger than 850 μm. This is named a comparative water-absorbing agent(4). The various properties of the comparative water-absorbing agent (4)as obtained are listed in Tables 2 and 3.

Comparative Example 5

To 100 parts of the water-absorbent resin particles (C-1) as obtained inComparative Referential Example 1, 20 parts of 30% aqueous solution ofpolyethylenimine (number average molecular weight: about 70,000,produced by Nippon Shokubai Co., Ltd.) was added to blend them, and theywere heat-dried at 120° C. for 10 minutes. Thereafter, the resultantmixture was classified with a sieve having a mesh opening size of 850μm, thus obtaining particles of not larger than 850 μm. To theseparticles, 1 part of silicon oxide of super-fine particle (produced byNippon Aerosil Co., Ltd., commercial name: Aerosil 200) was furtheradded to blend them. This is named a comparative water-absorbing agent(5). The various properties of the comparative water-absorbing agent (5)as obtained are listed in Tables 2 and 3.

Comparative Example 6

Making reference to Example 3 as described in JP-A-509591/1997, itstracing test was carried out in the following procedure:

To a Kitchen-type mixer, 100 g of the water-absorbent resin particles(C-2) as obtained in Comparative Referential Example 3 was added. Asolution, which comprised 10 g of 10 weight % polyallylamine (commercialname: PAA-10C, weight-average molecular weight: about 10,000, producedby Nitto Boseki Co., Ltd, and cation density: 17.1 mmol/g) and 20 g ofethanol, was prepared. After a portion of the solution was sprayed ontothe absorbent gel-formable particles with a spraying apparatus, themixer was operated for about 4 minutes. The spraying and mixingprocedure was repeated until the total of the solution was sprayed ontothe absorbent gel-formable particles. The resultant mixture was driedunder vacuum at 100° C. for about 3 hours. The resultant dried absorbentmaterial was pulverized with a hammer pulverizer and classified with astandard #20-mesh sieve (850 μm), thus obtaining particles passingthrough the standard #20-mesh sieve. These are named a comparativewater-absorbing agent (6). The various properties of the comparativewater-absorbing agent (6) as obtained are listed in Tables 2 and 3.

Comparative Example 7

Making reference to Example 2 as described in JP-A-3123/1997, itstracing test was carried out in the following procedure:

To 100 parts of the water-absorbent resin particles (C-2) as obtained inComparative Referential Example 3, 5.5 parts of 43% hydrochloridesolution (70 mol % neutralized product) of polyethylenimine(number-average molecular weight: about 70,000, and produced by NipponShokubai Co., Ltd.) was added to blend them, and they were kept in ahot-wind-dryer of 90° C. for 20 minutes after the blending. Thereafter,the resultant mixture was passed through a metal gauze having an openingsize of 840 μm, thus obtaining a water-absorbing agent. This is named acomparative water-absorbing agent (7). The various properties of thecomparative water-absorbing agent (7) as obtained are listed in Tables 2and 3.

As is described in Tables, the water-absorbing agents as obtained inExamples exhibited a high GV and a high AAP, and an excellent 16 hrPT,0.5 hrPT, BBS, 16 hrBBS, ΔPT, and DBBS. Among these, the water-absorbingagents as obtained by comprising the crosslinked cationic polymercompound as described in Examples 1 to 3, and as obtained by comprisingthe cationic polymer compound as described in Examples 6 to 11 areparticularly excellent in the effects. In Comparative Example 1 asobtained in Comparative Examples, the water-absorbing agent was producedwithout blending the water-absorbing resin particles (A) and thecationic polymer compound (B) together. Therefore, its 16 hrPT, 0.5hrPT, BBS, and 16 hrBBS were worse. In Comparative Examples 2 and 5among the comparative water-absorbing agents, the water-absorbing agentsdo not have a sufficient AAP as a water-absorbing agent because the AAPof the water-absorbent resin particles as used are lower. In ComparativeExamples 3 and 4, the water-absorbent resin particles as used exhibit ahigh GV and a high APP, but the cationic polymer as used is notfavorable. Therefore, its 16 hrPT, 0.5 hrPT, BBS, and 16 hrBBS wereworse. In Comparative Examples 6 and 7, the water-absorbent resinparticles exhibit a low FRUP and a low SFC, and the cationic polymercompounds as used are not proper because they are not uncrosslinked.Therefore, the sufficient performance could not be obtained in 16 hrPT,0.5 hrPT, BBS, and 16 hrBBS. FIG. 6 described photos of thewater-absorbing agent 1 and the comparative water-absorbing agent 2before or after pressurization when the 16 hrPT is measured. In thewater-absorbing agent 1, the water-absorbing agent aggregate hardlydeforms because it has an excellent shape-maintaining property. However,the shape of the comparative water-absorbing agent 2 was deformed.

In the above way, as is also apparent from Examples of the presentinvention, the water-absorbing agent and its production processaccording to the present invention provide: a novel water-absorbingagent of which the GV, AAP and SFC are also excellent, which has anexcellent shape-maintaining property or BBS of a water-absorbing agentaggregate after swelling, and maintains the effects for a further longtime after water is absorbed.

TABLE 1 Water-absorbent GV AAP FRUP resin particles (A) (g/g) (g/g)(second) SFC* A-1 25.6 22.4 70 101 A-2 29.2 25.1 220 40 C-1 34.1 8.22000 2 C-2 28.2 21.3 1214 10 *Unit (10⁻⁷ × cm³ × s × g⁻¹)

TABLE 2 Water- absorbent Cationic resin polymer Water-absorbing agentparticles compound GV AAP 16 hrPT (A) (B) Number (g/g) (g/g) (cm)Example 1 A-1 B-1 (1) 25.1 20.1 7.8 Example 2 A-1 B-2 (2) 24.0 20.0 8.7Example 3 A-2 B-1 (3) 28.5 24.1 8.5 Example 4 A-1 PAA-HCl (4) 25.0 22.012.0 Example 5 A-2 PEI + Si (5) 26.1 20.5 8.0 Example 6 A-1 PVAD (6)25.2 21.0 7.9 Example 7 A-1 B-3 (7) 25.4 22.1 9.5 Example 8 A-1 B-4 (8)25.3 21.5 8.5 Example 9 A-1 PVAD + (9) 25.5 21.4 9.3 Si Example 10 A-1PR8106 (10)  25.2 21.1 9.9 Example 11 A-1 PVAD-L (11)  25.3 21.0 9.0Comparative A-1 None Compar- 25.6 22.4 17.0 Example 1 ative (1)Comparative C-1 PEI Compar- 28.5 7.6 15.0 Example 2 ative (2)Comparative A-1 D-1 Compar- 24.9 23.0 17.0 Example 3 ative (3)Comparative C-1 EDA Compar- 32.5 8.3 16.0 Example 4 ative (4)Comparative C-1 PEI + Si Compar- 32.3 6.1 14.5 Example 5 ative (5)Comparative C-2 PAA Compar- 27.5 21.1 15.7 Example 6 ative (6)Comparative C-2 PEI-HCl Compar- 27.3 19.0 10.8 Example 7 ative (7)PAA-HCl: Polyallylamine hydrochloride, PEI + Si: Polyethylenimine +Aerosil 200, PVAD: Polyamidine (produced by HYMO, commercial name:Himoloc ZP-700), PVAD + Si: Polyamidine + Aerosil 200, PR8106: Partiallyhydrolyzed poly(N-vinylformamide(produced by BASF, commercial name:CatiofastPR8106), PVAD-L: Polyamidine (produced by Dia-Nitrix Co., Ltd.,commercial name: PVAD-L), PAA: Polyallylamine, PEI: Polyethylenimine,EDA: Ethylenediamine, PEI-HCl: Polyethylenimine hydrochloride

TABLE 3 Water-absorbing agent 0.5 Δ 16 hrPT PT BBS hrBBS DBBS NumberSFC* (cm) (cm) (gf) (gf) (%) Example 1 (1) 154 7.4 0.4 226 210 7.1Example 2 (2) 130 8.5 0.2 170 155 8.8 Example 3 (3) 92 8.4 0.1 190 1776.8 Example 4 (4) 130 8.7 3.3 220 133 39.5 Example 5 (5) 60 8.7 −0.7 189135 28.6 Example 6 (6) 121 7.7 0.2 170 175 −2.9 Example 7 (7) 131 9.30.2 178 183 −2.8 Example 8 (8) 128 8.6 −0.1 225 220 2.2 Example 9 (9)158 9.5 −0.2 131 130 0.8 Example 10 (10)  152 10.4 −0.5 125 125 0.0Example 11 (11)  163 9.1 −0.1 134 137 −2.2 Comparative Compar- 101 17.00.0 30 28 6.7 Example 1 ative (1) Comparative Compar- 10 15.0 0.0 75 5033.3 Example 2 ative (2) Comparative Compar- 120 17.0 0.0 34 30 11.8Example 3 ative (3) Comparative Compar- 2 16.0 0.0 25 21 16.0 Example 4ative (4) Comparative Compar- 10 9.2 5.3 183 75 59.0 Example 5 ative (5)Comparative Compar- 45 11.0 4.7 124 70 43.5 Example 6 ative (6)Comparative Compar- 21 6.7 4.1 250 118 52.8 Example 7 ative (7) *Unit(10⁻⁷ × cm³ × s × g⁻¹)

Various details of the invention may be changed without departing fromits spirit not its scope. Furthermore, the foregoing description of thepreferred embodiments according to the present invention is provided forthe purpose of illustration only, and not for the purpose of limitingthe invention as defined by the appended claims and their equivalents.

1. A production process for a water-absorbing agent, which comprises thestep of blending 100 parts by weight of water-absorbent resin particles(A) and 0.01 to 10 parts by weight of a cationic polymer compound (B)together, wherein the cationic polymer compound (B) is obtained by aprocess including the step of crosslinking a cationic polymer with acrosslinking agent of which the amount is 0.01 to 10 weight % of thecationic polymer, and wherein the cationic polymer compound (B) has awater solubility of 70 to 10 weight % if the cationic polymer compound(B) is obtained from an ethylenimine monomer, otherwise the cationicpolymer compound (B) has a water solubility of 100 to 10 weight %.
 2. Awater-absorbing agent, which is obtained by the production process for awater-absorbing agent as recited in claim
 1. 3. A water-absorbentstructure, which comprises the water-absorbing agent as recited in claim2.
 4. A production process for a water-absorbing agent, which comprisesthe step of blending 100 parts by weight of water-absorbent resinparticles (A) and 0.01 to 10 parts by weight of a cationic polymercompound (B) together, wherein the water-absorbent resin particles (A)exhibit an absorption capacity of not less than 20 g/g under a load of4.9 kPa (AAP) and a saline flow conductivity of not less than20(10⁻⁷×cm³×s×g⁻¹)(SFC), and wherein the cationic polymer compound (B)has a water solubility of 100 to 10 weight %.
 5. A water-absorbingagent, which is obtained by the production process for a water-absorbingagent as recited in claim
 4. 6. A water-absorbent structure, whichcomprises the water-absorbing agent as recited in claim
 5. 7. Awater-absorbing agent, which comprises water-absorbent resin particles(A) and a cationic polymer compound (B), wherein the cationic polymercompound (B) is substantially ionically bonded to the water-absorbentresin particles (A), with the water-absorbing agent being characterizedby exhibiting a free swelling capacity of not less than 23 g/g (GV), anabsorption capacity of not less than 20 g/g under a load of 4.9 kPa(AAP), and a saline flow conductivity of not less than50(10⁻⁷×cm³×s×g⁻¹) (SFC).
 8. A water-absorbing agent according to claim7, which exhibits a gel deformation of not more than 12.5 cm under ashort-time load (0.5 hrPT).
 9. A water-absorbing agent according toclaim 7, which exhibits a ball burst strength of not less than 80gf(BBS).
 10. A water-absorbing agent according to claim 7, wherein thecationic polymer compound (B) includes at least one member selected fromthe group consisting of polyamidines, polyvinylamines or salts thereofand partially hydrolyzed poly(N-vinylformamides) or salts thereof.
 11. Awater-absorbing agent according to claim 7, which further comprises aninorganic powder.
 12. A water-absorbent structure, which comprises thewater-absorbing agent as recited in claim
 7. 13. A water-absorbingagent, comprising a polymer prepared by polymerizing and crosslinking amonomer comprising acrylic acid and/or a salt thereof, wherein saidwater-absorbing agent exhibits a deterioration of ball burst strength(DBBS) of not more than 40%.
 14. A water-absorbing agent according toclaim 13, wherein said water-absorbing agent exhibits a gel deformationdeterioration of not more than 3.5 cm under a load with the passage oftime.
 15. A water-absorbing agent according to claim 13, comprisingwater-absorbent resin particles (A) and a cationic polymer compound (B).16. A water-absorbing agent according to claim 15, wherein said cationicpolymer compound (B) is obtained from an ethylenimine monomer having awater solubility of 70 to 10 weight %.
 17. A production process for aparticulate water-absorbing agent, which comprises the step of blending100 parts by weight of water-absorbent resin particles (A) and 0.01 to10 parts by weight of a cationic polymer compound (B) together, whereinthe water-absorbent resin particles (A) have a carboxyl group, comprisea crosslinked polymer obtained by polymerizing and crosslinking amonomer including acrylic acid and/or a salt thereof as a maincomponent, and exhibit an absorption capacity of not less than 20 g/gunder a load of 4.9 kPa (AAP) for a 0.9 weight % aqueous sodium chloridesolution (physiological saline) and a saline flow conductivity of notless than 20 (10⁻⁷×cm³×s×g⁻¹) (SFC), and wherein the cationic polymercompound (B) includes at least one member selected from the groupconsisting of primary amino groups, secondary amino groups, tertiaryamino groups, their salts, and quaternary alkylammonium salts and has awater solubility of 100 to 10 weight %.
 18. A production process for aparticulate water-absorbing agent according to claim 17, wherein thewater-absorbent resin particles (A) exhibit an uncrosslinkedwater-extractable content of not more than 15 weight %.
 19. A productionprocess for a particulate water-absorbing agent according to claim 17,wherein the water-absorbent resin particles (A) have a water content of0.1 to 10 weight % as measured according to a weight decrease by dryingthe water-absorbent resin particles (A) in an airless dryer of 180° C.for 3 hours.
 20. A production process for a particulate water-absorbingagent according to claim 17, wherein the water-absorbent resin particles(A) have a weight-average particle diameter of 300 to 650 μm (butexcluding 300 μm) and include fine particles of not larger than 149 μmin an amount of not more than 5 weight %, wherein the weight-averageparticle diameter is a weight-average particle diameter D50 determinedby first obtaining a particle distribution by classifying with JISstandard sieves of 850 μm, 600 μm, 300 μm, 150 μm, and 45 μm, and secondplotting the particle distribution on logarithmic probability paper. 21.A production process for a particulate water-absorbing agent accordingto claim 20, wherein the amount of the fine particles of not larger than149 μm in the water-absorbent resin particles (A) is not more than 3weight %.
 22. A production process for a particulate water-absorbingagent according to claim 17, wherein the water-absorbent resin particles(A) are surface-crosslinked ones.
 23. A production process for aparticulate water-absorbing agent according to claim 17, wherein thecationic polymer compound (B) has a weight-average molecular weight ofnot less than 10,000.
 24. A production process for a particulatewater-absorbing agent according to claim 17, wherein the cationicpolymer compound (B) has a cation density of not less than 2 mmol/g. 25.A production process for a particulate water-absorbing agent accordingto claim 17, which further comprises a step of adding an inorganicpowder in an amount of not more than 5 weight % of the water-absorbingagent in any stage of before, during, or after the water-absorbent resinparticles (A) and the cationic polymer compound (B) are blendedtogether.
 26. A production process for a particulate water-absorbingagent according to claim 17, wherein the cationic polymer compound (B)includes at least one member selected from the group consisting ofpolyamidines, polyvinylamines or salts thereof and partially hydrolyzedpoly(N-vinylformamides) or salts thereof.
 27. A production process for aparticulate water-absorbing agent according to claim 26, wherein thecationic polymer compound (B) includes at least one member selected fromthe group consisting of partially hydrolyzed poly(N-vinylformamides) orsalts thereof.
 28. A production process for a particulatewater-absorbing agent according to claim 17, wherein the water-absorbentresin particles (A) are granulated in said step of blending thewater-absorbent resin particles (A) and the cationic polymer compound(B) together, so that the weight-average particle diameter of thewater-absorbing agent as obtained is enlarged larger than that of thewater-absorbent resin particles (A).
 29. A production process for aparticulate water-absorbing agent according to claim 28, wherein theweight-average particle diameter of the water-absorbing agent asobtained is enlarged larger than that of the water-absorbent resinparticles (A) by 30 to 150 μm.
 30. A production process for aparticulate water-absorbing agent according to claim 17, wherein thesaline flow conductivity (SF) of the water-absorbent resin particles (A)is not less than 75 (10⁻⁷×cm³×s×g⁻¹).
 31. A production process for aparticulate water-absorbing agent according to claim 17, wherein thecationic polymer compound (B) is a crosslinked one.
 32. A productionprocess for a particulate water-absorbing agent according to claim 17,wherein the blending of the water-absorbent resin particles (A) and thecationic polymer compound (B) is carried out after a mixture of awater-absorbent resin and a crosslinking agent is heat-treated to obtainthe water-absorbent resin particles (A), or after a mixture of awater-absorbent resin and a crosslinking agent is heat-treated and theresultant water-absorbent resin particles (A) are cooled.
 33. Aproduction process for a particulate water-absorbing agent according toclaim 17, wherein the water-absorbent resin particles (A) of 60 to 200°C. and the cationic polymer compound (B) of 0 to 100° C. are blendedtogether.
 34. A production process for a particulate water-absorbingagent according to claim 17, wherein the water-absorbent resin particles(A) have a bulk density of not less than 0.5 g/ml.